Northampton inflicted a first away defeat of the season on Premiership leaders Harlequins.
Ryan Lamb landed an early penalty and drop-goal to put the hosts in front before Ben Foden went over while Nick Easter was sin-binned.
Rory Clegg slotted a penalty in response to two more Lamb kicks.
After the break Roger Wilson's converted try and some ferocious defending by Saints ensured they strengthened their position in third.
Under the gaze of England's interim head coach Stuart Lancaster, and with the Six Nations squad announcement days away, the match-up of England talent across both sides promised much.
The opening 10-minute spell was all Quins but their attacking intent was nullified by intense Saints defending and the hosts drew first blood when Lamb landed a 25m penalty after Luke Wallace hit a ruck from the side.
Saints then completely dominated nearly all of the first half as first Tom Wood and Foden came close to crossing and then the Saints pack were inches short after a steam-rollering maul from a five-metre line-out.
Quins infringed and Saints repeated the play, resulting in Nick Easter receiving a yellow card for dropping the maul.
Northampton upped the tempo even more and Lamb added a well-taken drop-goal.
Saints were bossing the breakdown and were rewarded when the ball found Foden on the right wing and he fended off his England full-back rival Mike Brown to slide into the corner.
Quins could not get out of their half, were losing out in the scrums and it was an infringement at the set-piece that saw Lamb give Saints a 14-0 lead from 35m.
Chris Robshaw, who was superb throughout, charged down Lamb's kick and ran in-field to allow Clegg to pull back three points for Quins with five minutes of the half left.
The visitors tried to assert themselves but Saints slowed their ball brilliantly and won successive penalties - the last of which Lamb slotted on the stroke of half-time.
Clegg missed an early shot at goal after the break before Saints conceded three quick-fire penalties at the breakdown but Dylan Hartley escaped a certain sin-binning.
The hosts were given a second let-off when Clegg sent another three-pointer wide.
And Quins were made to pay when Northampton pulled them first right and then back left before Lamb sent Wilson over from 10 yards and then added the conversion to make it 24-3.
Mark Sorensen, on his 100th Premiership appearance, was then sin-binned for coming in from the side.
But despite their numerical advantage Quins were forced into silly mistakes by Saints, with Lee Dickson a constant thorn in their side.
Danny Care produced a sycthing break in the closing 10 minutes as Harlequins pushed for a try but Saints' superb defensive work held them out.
Northampton director of rugby Jim Mallinder:
"We've been building towards that and we've had some good halves of rugby but I think today we were all round a good team in terms of our tempo and our attacking play.
"Defensively we shut them up and stopped them playing, which of course they are good at, so we're very pleased.
"Ryan [Lamb] was excellent. His decision making was outstanding; he's maturing rapidly and Lee [Dickson] has been very good for us and is actually getting better. I have described him as being the heartbeat of Northampton."
Harlequins director of rugby Conor O'Shea:
"They were just more physical than we were and they won the contact and collision area.
"If you come here and don't get momentum then you're going to be in for a tough night. They were outstanding and we weren't.
"For the first time this season there was an 80 minutes where we haven't actually performed, but that happens."
Northampton: Foden; Ashton, Pisi, Downey, Cato; Lamb, Dickson; Tonga'uiha, Hartley, Doran-Jones; Manoa, Sorenson; Dowson, Wood, Wilson.
Replacements: Haywood, Waller, Mujati, Day, Nutley, Roberts, Myler, May.
Harlequins: Brown; Williams, Hopper, Turner-Hall, Monye; Clegg, Care; Marler, Brooker, Johnston; Kohn, Robson; Robshaw, Wallace, Easter.
Replacements: Gray, Lambert, Fairbrother, Vallejos, Guest, Bolt, Urdapilleta, Smith.
Referee: Dave Pearson (RFU)