A place in the semi-finals of the Powergen Cup is in the bag after the weekend's win over Sale Sharks but now it is approaching make-or-break time for Simon Easterby's team in their challenge to reach the knock-out stages of the Heineken Cup for the sixth time, with the 11th final of the tournament being staged at the Millennium Stadium on 20 May, 2006.
Defending champions Toulouse top Pool 6 with seven points, Edinburgh Gunners are next on five points followed by the Scarlets on four and 2004 champions Wasps on three points.
"It has been a tough year so far so it was important to win and get to the Millennium Stadium for the double-header Powergen Cup semi-finals in the new year," said Scarlets coach Nigel Davies.
"Now we are focused on what is a vital Heineken Cup game that both sides will be desperate to win. For the losers, it could be the end of their Heineken Cup hopes for another year. It is that big.
"Both of us have great traditions in the Heineken Cup - although they are one up on us by having won the trophy in 2004 - and Wasps are right up there with the best. They have to be on of the top two or three sides in Europe and they will come with all guns blazing.
"As far as I am concerned, we have to step up tenfold on the performances of our last two home games - and I am determined we will do just that. You will see a completely different side on Sunday.
"We have put some good rugby together this year but in our last two home games, against Edinburgh in the Heineken and then against Sale at the weekend, we have not played at all well. We have under performed in those games but still won.
"By contrast we have played some superb stuff on the road, such as at Munster, and lost. We need to put both those elements together against Wasps.
"It is very difficult to pinpoint any weaknesses in their side and I have a huge respect for their rush defence, which they do so very well, and their ability to break up the game across the park."
Wasps rescued their Heineken Cup campaign when they snatched a last gasp 15-15 draw at home to Toulouse in Round 2 while the Scarlets pipped Edinburgh 15-13 at Stradey Park to keep their hopes alive
The Scarlets and Wasps have met just twice in the Heineken Cup, results in the 1999 / 2000 tournament going with home advantage.
Meanwhile, on top of the result against the Sharks, the big plus for the Scarlets was the return to action of fit-again British and Irish Lions and Wales scrum half Dwayne Peel.
"Dwayne came on about 10 minutes into the second half and was instrumental in upping the tempo of the game and getting us more width and pace into our game," said Davies.
"He has been brilliant for us, his country and the Lions over the past 15 months and now he has this fabulous air of confidence about his ability to produce the goods.
"The fact that we had not had a game for five weeks contributed to the poor performance against the Sharks but now we have to make a massive improvement for the Wasps challenge."
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