Harlequins director of rugby Conor O'Shea hailed his team's attitude after they ended Biarritz's unbeaten home record with a 16-9 victory in the Heineken Cup.
Quins completed a clean sweep in Pool 3 with a hard-earned victory at rain-soaked Parc des Sports Aguilera. Tom Guest grabbed the game's only try while the tactical and goal-kicking of Nick Evans, who scored 11 points, proved decisive.
It was only the second home defeat in the last 35 European games for Biarritz, who could only manage three Dimitri Yachvili penalties. O'Shea said: "It was a mature performance and we are delighted with the attitude of the players."
He added: "There was a lot of experience out there of playing together and in tough conditions but it was one of those nights when you had to roll the sleeves up and show as a group what it means to play for each other. We had to grind it out.
"We knew the kicking duel would be crucial and Nick Evans, Danny Care and Mike Brown kept us playing in the right areas.
"To come to the south of France and get a win against any team is outstanding, especially given that's only the second time in the Heineken Cup that Biarritz have been beaten here.
"That was the motivation for the players as well as aiming to be number one seeds for the quarter-finals which could be important."
Harlequins are guaranteed a home tie in the quarter-finals and only Toulon and Clermont-Auvergne can now deny them top seeding for the knock-out stage.
O'Shea added: "Momentum is great in rugby and it was good to carry on the winning habit. It's also great for the fans who came out to watch us and all those back home who now have something special to look forward to. There's a lot of rugby to be played before the quarter-final but we're looking forward to April."
Defeat ended Biarritz' slim hopes of progressing, though the 2006 and 2010 finalists could still qualify for the Amlin Challenge Cup as one of three group runners-up.