Connacht pushed Harlequins all the way as the Aviva Premiership leaders hung on to this season's 100 per cent record with a 25-17 Heineken Cup victory.
The Irish side scored two tries to one but an immaculate 20-point goal-kicking display from fly-half Nick Evans edged Quins to their 11th successive victory of the campaign.
Scrum-half Karl Dickson scored Quins' only try as they set a club record best start to a season, overtaking their 10 wins in both the 1954-55 and 1996-97 seasons.
Spirited Connacht replied with tries from left-wing Tiernan O'Halloran and their former Harlequins full-back Gavin Duffy. Fly-half Miah Nikora landed a penalty and conversion before his replacement Niall O'Connor contributed a penalty.