Northampton moved provisionally top of the Aviva Premiership table after beating Harlequins 23-9 on Friday.
Second-half tries from George North and Dylan Hartley lit up a game which was dominated by the packs, as the Saints picked up a vital win.
Northampton are top, for a day at least, and will take confidence from the fact that they have now beaten the other three teams in the play-offs so far this season.
Quins could drop out of the top four if Leicester pick up a win on Saturday afternoon, as they left Franklin's Gardens without a losing bonus-point.
The Saints looked to dominate the early proceedings, building up 12 phases in the Harlequins 22 before winning a penalty which Stephen Myler slotted from in front of the posts.
Nick Evans was on hand to cancel out the hosts' lead, with three points taken from Quins' first foray into the opposition half.
After the early points, chances were at a premium for both sides until midway through the half.
Harlequins were inches away from scoring the first try of the night, camping on the Saints line for a sustained period, with Chris Robshaw going close before they eventually settled for three points.
Myler's leveller on the stroke of half time kept the game tightly balanced with a 6-6 half time score.
The game needed North's try to create the first major cheer of the night. After bouncing off Charlie Walker, The Welsh international was given a free run to the corner which he gleefully took to dive over. Myler's super conversion added the icing to the cake.
Myler appeared to be struggling with an injured foot though, and showed signs of struggling when he missed one of the easier kicks he will ever be given, skewing wide from close range.
Ben Botica's three pointer had the game on a knife edge with just four points separating the two teams going into the last 15 minutes.
Former league man Myler bounced back from his earlier miss soon after as Northampton edged closer to victory.
Hartley's try with ten minutes left put some gloss on the scoreline, and starved Harlequins of a bonus point. The England man was in the right place in the right time when Quins failed to retain possession despite looking to have stolen a lineout.
Tries: North, Hartley
Con: Myler 2
Pen: Myler 3
Pen: Evans 2, Botica
Northampton: 15 Tom Collins, 14 Jamie Elliott, 13 George Pisi, 12 Luther Burrell, 11 George North, 10 Stephen Myler, 9 Lee Dickson, 8 Samu Manoa, 7 Phil Dowson, 6 Calum Clark, 5 Christian Day 4 Courtney Lawes, 3 Salesi Ma'afu, 2 Dylan Hartley (c), 1 Alex Wakker.
Replacements: 16 Mike Haywood, 17 Ethan Waller, 18 Tom Mercey, 19 Sam Dickinson, 20 Tom Wood, 21 Kahn Fotuali'i, 22 Glenn Dickson, 23 Fa'atoina Autagavaia.
Harlequins: 15 Mike Brown, 14 Charlie Walker, 13 Matt Hopper, 12 Tim Molenaar, 11 Sam Smith, 10 Nick Evans, 9 Karl Dickson, 8 Nick Easter, 7 Chris Robshaw (c), 6 Tom Guest, 5 George Robson, 4 Charlie Matthews, 3 Will Collier, 2 Dave Ward, 1 Joe Marler.
Replacements: 16 Max Crumpton, 17 Mark Lambert, 18 Paul Doran Jones, 19 Nick Kennedy, 20 Joe Trayfoot, 21 Sam Stuart, 22 Ben Botica, 23 Ollie Lindsay-Hague.
Referee: Greg Garner
Assistant referees: Paul Dix, Paul Burton
Television match official: David Grashoff