Harlequins director of rugby Connor O'Shea praised the "mature attitude" of his players after their hard-fought 16-9 win at Biarritz.
Quins made it six wins out of six in Heineken Cup Pool 3 as Biarritz suffered only their second defeat in their last 35 European games.
Tom Guest scored the game's only try while all-round kicking of Nick Evans, who scored 11 points, proved decisive.
O'Shea said: "It was a mature performance and we are delighted with the attitude of the players.
"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 No 1 seeds for the quarter-finals which could be important.
"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."
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