The Llanelli Scarlets’ opening game of the competition began with a home defeat at the hands of Toulouse. In a game of missed opportunities the former Heineken Cup Champions barely touched the touched the ball in the first half as the Scarlets dominated but could not transfigure the pressure into points. Arwel Thomas, who scored all the points in the Scarlets defeat, missed three relatively easy attempts which opposite number Jean-Baptiste Elissalde punished; he converted a further penalty to close the scores at 6-9 in a game that the Scarlets should have won. Drawn against the Northampton Saints for the second successive competition, the Scarlets suffered a 25-3 defeat away from home as the Saints enacted revenge for their two defeats in the 2003–2004 tournament. Arwel Thomas was only able to add a penalty for the Welsh region as metronomic kicking from Paul Grayson, along with three tries, kept Northampton firmly in control.

The Scarlets next travelled to Hughendon to face the Glasgow Warriors knowing that a win was crucial to retain any hope of progressing to the latter stages of the tournament. The away side attained four tries and the resulting bonus point in a strong first half performance but had to withstand a valiant second-half comeback from the Scots. Despite a last minute scramble, the Scarlets preserved their narrow 26-29 advantage to secure their first win in the competition that season thus far, and ended the Warriors’ Cup hopes to boot. In the return leg fixture the Scarlets amassed more points in their second win over Glasgow in a week but again showed signs of weakness. In scoring five tries, a brace each for Aisea Havili and Tal Selley, the Scarlets obtained a vital bonus point but many missed opportunities and two sin-binnings would have worried coach Gareth Jenkins. Despite the indiscipline shown in the match the Scarlets had achieved their second win over a battling Scottish side, who scored three tries albeit consolatory ones.

Round Five saw the Scarlets suffer their second defeat by Northampton, which effectively ended their 2004-2005 Heineken Cup campaign. The match was played in difficult conditions and so the efforts of the goal kickers were key. Gareth Bowen secured five penalties for the home side whilst Gavin Thomas crossed the line to put the home side 20-12 ahead. Yet once more the veteran fly-half Paul Grayson proved a potent force and kept the Saints in contention before Steve Thompson clinched the win in the dramatic finale as he secured an eleventh hour try. Grayson added the conversion to nudge the Saints ahead and they claimed a 20-22 victory to quash Scarlet hopes of emulating their previous year’s quarter-final berth. The Scarlets’ concluding pool stage encounter rounded off their disappointing competition with a 53-36 loss to eventual 2004-2005 winners Toulouse. In their eight-try performance Toulouse cemented their position as one of the tournament favourites as the Scarlets bravely battled to secure five tries of their own, including a brace from Chris Wyatt. Trailing 33-17 at the interval the region were unable to overthrow their stronger hosts in the second half; the Scarlets ended their competition on a low note having failed, with only two wins from six, to progress from the Pool.

The Ospreys had been drawn in Pool Four against Castres Olympique, the NEC Harlequins and Munster; only the latter of whom was seeded, compared to the two seeded teams in the Scarlets’ pool. In their opening clash the Ospreys met Castres at the Stade Pierre-Antoine and faced a rampant French side. Castres led 23-7 at half-time and secured more tries in the second half to gain an important bonus point. Tries from Jason Spice and Adam Jones proved only consolatory for the Ospreys who were outclassed by a tidier and more committed side that won 38-17. Round Two saw the Ospreys host Irish giants Munster at the Gnoll as they incurred their second defeat of the tournament. Despite a half-time lead of 12-9 the Ospreys conceded a Ronan O’Gara try and could not break the 18-20 deficit to overcome the Irish.

Round Three brought the Ospreys their first win of the tournament, at home to the NEC Harlequins. The visitors scored a first minute try, courtesy of Tom Williams, but eight penalties from the boot of Gavin Henson secured the home side’s 24-7 victory. Man-of-the-match Henson proved a crucial Ospreys member in the return leg fixture a week later at The Stoop. Gathering a twenty-six point haul, including a try in each half of the match, Henson strengthened the Ospreys’ 19-46 victory and their quarter-final qualification hopes. Though the Harlequins fought well in the first-half, including a try for England centre Will Greenwood, after the interval the Ospreys powered through to a six-try bonus point victory, aided by the fact that the Quins had three members sin-binned.

With the Ospreys in a good position for the knock-out stages they travelled to Ireland to take on Munster in Round Five of the competition. The Irish retained their unbeaten home record in the European competition with a 20-10 defeat of the Welsh region; outscoring the Ospreys by two tries to one. The Ospreys had the stronger last thirty minutes of the match but the determined Irish defence kept out the visitors to aid their chances of reaching the latter stages of the tournament, whilst dashing the hopes of Welsh advancement. The last game of the Ospreys’ 2004–2005 tournament saw them host Castres at The Gnoll. With a 20-11 defeat of the French side to avenge their first round crushing, the Ospreys denied Castres a runners-up position in the Pool to send them out of the competition. The Welsh region fought back from a 10-11 deficit at half-time; a try from Elvis Seveali’i cemented the win in injury time. The Ospreys finished the tournament on a high note but in reality finished in the bottom half of the table with only three wins from six.

The Newport Gwent Dragons faced a tricky Heineken Cup campaign having been drawn against the Newcastle Falcons, Edinburgh Rugby and Perpignan. They encountered the Zurich Premiership side in their opening encounter in driving wind and rain at Rodney Parade. An error from Kevin Morgan gifted the Falcons’ Mike McCarthy a try which proved to be the decisive score in the game. Luke Gross was sent off in an encounter with Ian Gough mirroring his surname but the Dragons were unable to capitalise on this advantage as the final score closed at 6-10. The Dragons travelled to Murrayfield for Round Two of the competition and pulled out a narrow 13-17 win over the Scots. The score at the interval rested at ten points apiece following tries from Gareth Wyatt and Dougie Hall for Edinburgh. The second half saw a further Dragons’ try scored by Hal Luscombe and although Chris Paterson pulled a penalty back for the Scots the Dragons held on to grind out their first win of the competition.

Looking to build on their win in Scotland the Dragons next entertained Perpignan at Rodney Parade. The Dragons improved on their 10-0 lead at the interval to overcome the French side by 27-14 in a four-try, bonus point winning display. Man-of-the-match Gareth Cooper bagged one of the four tries whilst Sione Tuipulotu secured the final try, and consequent bonus point, with eleven minutes remaining as the French defence retreated. A reversal of fortunes was dealt to the Dragons on the second meeting with Perpignan at the Stade Aime Giral a week later. The French side avenged their previous defeat with a 32-9 victory over the Welsh region that crushed their Heineken Cup dreams. Three converted tries in the first fifteen minutes powered Perpignan ahead with Ceri Sweeney only able to reply with three penalties. The Dragons failed to add to their score in the second half whilst Perpignan hooker Jan van den Heever crossed the Welsh region’s line to secure the bonus point for his side.

Round Five saw the Dragons host Edinburgh at Rodney Parade and secure their second win over the Scots in the tournament. The impressive 48-5 scoreline ensured a bonus point for the Welsh region in a game which kept their qualification hopes alive. Four first-half tries from the Dragons put the game out of Edinburgh’s reach as they could only respond with a single unconverted try. The rout was completed after the interval as Jason Forster and Gareth Wyatt each accomplished their brace of tries and Gareth Baber and Adam Black made it eight tries to one in the powerful performance. The Dragons travelled to Newcastle for the final round match in which they suffered another defeat at the hands of the English side. The Falcons took an early lead due to the boot of Australian fullback Matt Burke and a try from Colin Charvis though Gareth Wyatt’s try reduced the deficit to 13-5 at the half-time whistle. On the resumption of the game Tom May and Kevin Morgan exchanged a try each to take the scores to 18-12 but Burke proved the crucial player as he secured a try and converted his own effort to put the Falcons out of reach. Though Ian Gough obtained a try afterwards it was little more than consolatory for the Dragons, who had again missed out on a quarter-final berth in the Heineken Cup competition due to this 25-17 loss.

The Cardiff Blues were drawn in Pool Six with third-seed team Stade Francais, Irish giants Ulster and Gloucester Rugby. Away to Ulster in their opening clash the Welsh region suffered their first defeat of the tournament. Despite a try from Tom Shanklin the Irish side were ultimately unreachable due to the superb goal-kicking performance provided by fly-half David Humphreys. Scoring five penalties and two drop goals he enjoyed a one hundred per cent success record to secure a 21-16 victory. The Blues suffered their second successive defeat in the Cup tournament at home to Stade Francais. A brace of tries for Dean Dewdney were cancelled out with the four-try scoring effort from Stade, including a superb Julien Arias effort in which he ran the length of the field. Gonzalo Quesada added the fourth and subsequently earned a bonus point for the French whilst the ever-reliable boot of David Skrela ensured the French side retained control of the game, and of Pool Six.

Having lost the first two games of the competition the Blues travelled to Gloucester to make it three losses out of three in a hard-fought and narrow loss at Kingsholm. The Blues led 16-10 at the interval but a second-half try from James Bailey and the second of a brace from Terry Fanolua secured the game for the English team. The final score rested at 23-19 with the Blues unlucky not to get more than a losing bonus point out of the fixture. Gloucester completed the double over the Blues a week later in Cardiff as they pulled out a 16-23 victory. In a match that saw four sin-binnings, three to one in favour of the visiting side, Gloucester took the narrow 6-7 lead into the half-time interval. Andy Goodridge added a try in the second half to stretch the lead further with the boot of Henry Paul aiding and abetting. Craig Morgan obtained a late try for Cardiff to claim a losing bonus point but it provided little bonus for the Blues’ fans as they had witnessed their team exit the competition with two matches still remaining.

The Blues faced the arduous task of an away-from-home encounter with Pool leaders Stade Francais in Round Five of the competition. An under-strength Blues side battled it out against the French team and had the majority of early territory. They led twice in the opening quarter of the game before Julien Arias bagged his first of a brace of tries on the nineteenth minute. He added his second before the interval and with the help of David Skrela’s boot extended the French side’s lead to 21-9 on the half-time whistle. The Blues applied pressure on the resumption of the game but Stade Francais scored their third try ten minutes after the interval. John Yapp grabbed a consolatory try for the Blues with four minutes remaining but this was cancelled out by Stade’s fourth try in injury time, which secured the vital bonus point for the leaders of Pool Six. The final round of the Cardiff Blues’ Heineken Cup competition saw them entertain Ulster at the Arms Park. In their sole victory of the 2004–2005 tournament the Blues pulled a win out of the bag to give the Cardiff crowd something to cheer in an otherwise disappointing European display. The Blues headed into the second half leading narrowly at 6-3 after a quiet first-half display. David Humphreys soon equalised matters but tries from Jonny Vaughton and Rhys Thomas gave the home side the advantage; Ulster could only secure another two penalties to take the final score to 16-12.

For the first time in the tournament’s history no Welsh representative had progressed into the quarter-final stages of the competition. The Scarlets failed to emulate their quarter-final qualification of the previous year whilst the other three regions were still waiting for a berth in the latter stages of the tournament in their new regionalised structures. Welsh interest in the elimation stages of the competition was, as with the previous season, left to the appearance of a Wales Captain in the final, and on the winning side.

Gareth Thomas's part for Toulouse in the Heineken Cup final of 2005 at Murrayfield was not as pivotal as Rob Howley's at Twickenham for Wasps the previous season, but nonetheless, he did end up celebrating on the winners' podium with the Heineken Cup in his hands. In a game that became a story of traded penalties and drop goals, Thomas, who had joined Toulouse at the end of the 2003-2004 season, very nearly provided the only try of the match. Early in the proceedings, he attempted to squeeze through the Stade Francais line; an opportunity created by a chip from Frederic Michalak. It was the Frenchman who proved the match winner in the end, pulling Toulouse level close to full time before dropping a winning goal in extra time. Thomas capped his Wales Grand Slam with European rugby's top prize.