Northampton stay on top
Northampton remained top of the Aviva Premiership with a hard-fought victory before a sell out crowd of 82,000 at Twickenham.
Quins took an early 8-0 lead and were the much better side in the first half but they could not take advantage even when the Saints lost Salesi Ma'afu to the sin-bin.
The second half was far more even but Northampton were the more clinical to come away with victory.
Northampton's tries came from Samu Manoa, George North and Kahn Fotuali'i with Stephen Myler kicking three penalties and three conversions.
Harlequins responded with tries from George Lowe, Jack Clifford and Sam Twomey with Tim Swiel kicking two penalties and two conversions.
Both teams made five changes to their starting line-up despite winning last week's fixtures. Quins recalled Ugo Monye and Danny Care in the backs together with Dave Ward, Will Collier and Nick Easter in the forwards. Nick Evans and skipper Joe Marler were still unfit so Easter led the side.
Northampton were also without their captain, Dylan Hartley, after he was sent off last week. Courtney Lawes was rested with Mike Haywood and Sam Dickinson taking their places. Behind the scrum, there were recalls for George Pisi, Ben Foden and Lee Dickson.
Quins took the lead after five minutes with a splendid try. From a line-out on half-way, Lowe made a huge break, brushing aside a weak tackle from Myler, to take his side into the opposition 22. Care made a quick dart to put the Saints further on the back foot before a long pass from Marland Yarde enabled Lowe to squeeze in at the corner.
Swiel missed the conversion but minutes later kicked a penalty before Saints got on the scoreboard with a Myler penalty. The outside half could have kicked another goal but Saints chose an attacking line-out as opposed to the option of another three points. They were immediately rewarded when Manoa drove over for the try which Myler converted for Northampton to lead 10-8 at the end of the first quarter.
That score line was against the run of play as Quins had seventy five per cent of possession and territory in that opening 20 minutes with Mike Brown and Lowe causing the visitors' defence major problems with their creative running.
After 33 minutes, Northampton suffered a blow when Ma'afu was shown a yellow card for a high tackle on Lowe but despite this setback, Quins extended their lead when Myler kicked his second penalty to give the Saints an undeserved 13-8 interval lead.
Early in the second half, Manoa was penalised for not releasing but Swiel could not take advantage by pushing his kick well wide. Moments later Swiel made another error by having his clearance charged down by Manoa. The number eight picked up the loose ball to send North over for the try which Myler converted.
Ma'afu returned from the sin-bin and his side nearly extended the lead when a careless pass from Care was intercepted by Ken Pisi. The wing had a long but clear run to the line but Swiel managed to bring Pisi down with a tap tackle.
Swiel and Myler exchanged penalties as Northampton attempted to keep a grip on the game with internationals, Kahn Fotuali'i and Alex Corbisiero being introduced from the bench.
However the hosts got back into contention when Swiel made a neat break and was hauled down inches short. Harlequins maintained their momentum for Clifford to cleverly step inside North for a try which Swiel converted to leave Northampton 23-18 ahead at the end of the third quarter.
Saints had three chances to extend that lead but chose line-outs in preference to kicks at goal but it proved to be the wrong call as Corbisiero lost possession as he dived over.
After 71 minutes, Northampton's forward dominance was rewarded when Fotuali'i crashed over but Quins had the final say when replacement Twomey scored their third try converted by Swiel.