Harlequins transferred their impressive Heineken Cup form into the Guinness Premiership as they outplayed Northampton at The Stoop.
They avenged a 23-13 defeat at Franklin’s Gardens in December to leave the Saints, unbeaten at home, still looking for their first Premiership away victory of the season.
South African hooker Gary Botha marked his return to the starting line-up after injury with a third-minute try for Quins.
A second-half penalty try, a touchdown by replacement lock Jim Evans and 12 points from the boot of former All Blacks fly-half Nick Evans completed the Quins scoring – Stephen Myler replying with two penalties for Saints.
Harlequins were without winger Ugo Monye, scrum-half Danny Care and number eight Nick Easter on England duty.
But Northampton appeared to miss Ben Foden, their line-breaking full-back or scrum-half, England second-choice hooker Dylan Hartley and injured Scottish prop Euan Murray more.
Lively former England scrum-half Andy Gomarsall, back for Quins in place of Care, was prominent as they launched a multi-phase attack which ended with Evans sending Botha over in the corner.
Evans landed the conversion from near the touchline and increased the home lead to 10-0 with an 18th-minute penalty, after French referee Christophe Berdos penalised the Northampton scrum.
Northampton were fortunate not to concede a second try when Scotland winger Sean Lamont ran into trouble and was dispossessed by as he strolled back after neglecting to touch down behind his own line, fielding a kick from Evans.
Quins moved the ball quickly from right to left but squandered their advantage when they were penalised at a ruck.
Saints, showing little in attack, missed their only first-half scoring chance when Myler was narrowly wide with a 45-metre penalty – before Evans struck with the final kick before the interval to stretch the lead to 13-0.
Former England winger David Strettle, returning from surgery on the broken metatarsal which had kept him on the sidelines since October, looked eager to make up for lost time as he went looking for the ball and caused Northampton problems with his elusive running.
There was a momentary scare for Strettle, who looked uncomfortable as he limped away from a tackle pointing to his right foot – but he appeared to run off the problem.
Botha was controversially denied a second try when the French official upset the home fans by ruling that the player had cannoned off him on his way to the line – and awarded Quins a scrum instead.
But there was no respite for Northampton – who conceded a 51st-minute penalty try, converted by Evans, as the Harlequins scrum drove them back over their own line.
Northampton finally opened their account after 54 minutes when Myler landed his third penalty attempt, and he was on target again four minutes later to reduce the deficit to 14 points.
But Quins put the issue beyond doubt when Jim Evans, capitalising on a break by his namesake, romped in for their third try in the 67th minute – with the fly-half adding his third conversion.