James Downey's second-half try handed Northampton victory at Franklin's Gardens as Harlequins were punished for their lack of discipline in. Downey struck with 20 minutes to go after Quins, with hooker Tani Fuga in the sin-bin, had lost the ball at the line-out.
Ugo Monye's try had put the visitors in control at the break, with Nick Evans continuing his impressive form with the boot after securing a memorable win over Stade Francais in the Heineken Cup last weekend. But after Jon Clarke's converted try levelled the scores, Andy Gomarsall and then Fuga were yellow carded and Downey burst clear.
Stephen Myler spurned the chance to kick Northampton ahead after two minutes when Evans, who slotted a last-gasp drop-goal to beat Stade Francais last weekend, knocked on.
The fly-half's kick crashed against the crossbar but after Will Skinner was penalised for not rolling away, Myler rediscovered his aim to fire Saints 3-0 ahead after seven minutes. Monye broke immediately from the restart and although Evans looked rusty in defence he made no mistake with the boot after Northampton were penalised to level the scores.
Myler restored Northampton's advantage after Quins were penalised for collapsing the scrum but the lively Monye responded with the first try of the game in the 20th minute. With both front-rows exchanging blows in the middle of the park Gomarsall released Monye - who broke from the left of the scrum to dot down unopposed, with Evans slotting the extras.
Northampton skipper Bruce Reihana almost responded in kind but he was tap-tackled with the line gaping and after Ignacio Fernandez Lobbe dropped the ball following an exchange of kicks, Evans fired over another penalty. The 28-year-old Kiwi almost replicated last weekend's game-winning kick with 20 seconds of the first half remaining but his attempted drop-goal drifted wide.
After wasting two chances to set Saints clear in the opening half, Myler released Scott Gray in the first minute of the second and the Scottish international fed Clarke to score with Myler levelling the scores. Reihana then kicked and chased only for Gomarsall, in for the rested Danny Care, to earn himself a yellow card with a deliberate block.
Myler missed the penalty attempt but Quins were forced to deploy Monye as an auxiliary fly-half which weakened their hand at the scrum. Sean Lamont and Paul Diggin combined to release first Soane Tonga'uiha and then Dylan Hartley before Harlequins eventually lost discipline and Fuga was sent to the sin-bin for deliberately killing the ball.
Myler swept over the simplest of penalties and with Fuga unavailable to throw the ball, Northampton stole Quins' line-out, allowing Downey to extend the home side's lead. Evans rounded off Harlequins' miserable second half by slicing two late penalties wide as Harlequins clung on for victory.
Northampton boss Jim Mallinder believes that his side can use today's win as a springboard to a positive result away to Bath next weekend. "We're on a good run, but we haven't been getting the results in the Premiership so we need to keep the momentum and get something at Bath next week," said Mallinder. "We're still learning lessons in the Premiership all the time. We're playing some good rugby at home but we still need to be smarter on the road.
"It's a good start to this period of games. We were pleased with the scrum and how that went because it was vital that we slowed Harlequins down. Dylan Hartley is competitive and aggressive and he's learning to look after himself. He's still young but you can see he's a good player.
"It's very nice to win and it's even better to win against a side who are playing so well at the moment."
With Andy Gomarsall's sin-binning such a crucial moment in the game, Harlequins boss Dean Richards faced some questions about his decision to rest the in-form Danny Care. "We had to rest Danny at some stage as he's part of the Elite Squad," said Richards. "We felt today was the right day to do it, as it has been a bruising few weeks for us and we can't just run him into the ground.
"I think we looked a bit tired. On the day we were a bit jaded. It's been a busy five weeks with some very difficult games and we didn't perform to the best of our ability. I don't think we were in control first half. Both sides didn't play well and it was a poor game of rugby.
"They came out more fired up in the second half and a couple of things went right for them. They played well and we have to take this onboard and learn from it."
Northampton: Reihana (capt); Diggin, Clarke, Downey, Lamont; Myler, Dickson; Tonga'uiha, Hartley, Murray, Fernandez Lobbe, Day, Easter, Gray, Wilson.
Replacements: Shields, Smith, Rae, Hopley, Foden, Spencer, Mayor.
Harlequins: Brown; Stegmann, Tiesi, Turner-Hall, Monye; N Evans, Gomarsall; C Jones, Fuga, Ross, Percival, J Evans, Robshaw, Skinner (capt), Easter.
Replacements: Brooker, Lambert, Robson, Guest, Williams, Malone, De Wet Barry.