Saints win at The Stoop
England hooker Dylan Hartley's 69th-minute try enabled Northampton to follow up their opening victory over Premiership champions Leicester Tigers with their first away win - 20-16 - over Harlequins for six years.
The Northampton captain took a short pass from scrum-half Lee Dickson to drive in from close range after Quins had moved ahead for the first time in the game at 16-13.
Chris Ashton, leading try-scorer in last season's Premiership, had earlier picked up where he left off as Northampton opened up a 13-0 first-half lead.
The England winger outpaced the Quins defence to touch down three minutes before half-time.
Harlequins paid heavily when full-back Mike Brown threw out a wayward pass as he was tackled by England lock Courtney Lawes.
The ball bounced off Quins team-mate Jordan Turner-Hall and Northampton centre James Downey hacked the ball deep into space for the chasing Ashton to kick on again before dropping on the ball over the try-line.
Fly-half Shane Geraghty, who kicked 10 points, converted to put Northampton 13-0 ahead.
Geraghty, a contender for the England number 10 shirt for the autumn internationals with first-choice Toby Flood, of Leicester, currently injured, also landed two first-half penalties from three attempts.
The win was Northampton's first over Harlequins at The Stoop since September 2004, although they did win the 2009 European Challenge Cup final there, beating French side Bourgoin 15-3.