Harlequins outscored Northampton Saints two tries to one to win 26 - 13 at the Stoop on Friday.
Sixteen points from the boot of fly-half Nick Evans saw Harlequins avenge last year's home defeat at the hands of Saints.
Evans' accuracy in front of goal kept the visitors to the Twickenham Stoop at bay in the first half as Harlequins went into the break leading 12-7.
Saints were behind with just three minutes on the clock for failing to roll away in the tackle, an offence they repeated at the end of the quarter, with Evans again making no mistake with the kick at goal.
But Jim Mallinder's men found themselves ahead when full-back Greig Tonks scored their only try of the evening and Stephen Myler converted. The lead was short-lived, though, as Evans took the two further chances that came his way.
Quins got their first try six minutes into the second period when a great break and offload from scrum-half Karl Dickson put in Joe Gray under the posts.
Evans was again on target with the conversion before Myler responded with three points of his own for Saints. Jordan Turner-Hall showed his class to set up Quins' second try, with a strong break that was finished off by England international Ugo Monye.
Quins soaked up the pressure that came their way after that to keep their line intact, although Ryan Lamb did manage to add a penalty for Saints. Sadly, for them, it proved too little too late, in contrast to last weekend's late kick that won the match against Gloucester.
Tries: Gray, Monye
Cons: Evans 2
Pens: Evans 4
Pens: Myler, Lamb
Harlequins: 15 Mike Brown, 14 Ross Chisholm, 13 George Lowe, 12 Jordan Turner-Hall, 11 Ugo Monye, 10 Nick Evans, 9 Karl Dickson, 8 Chris York, 7 Will Skinner, 6 Chris Robshaw (capt), 5 George Robson, 4 Ollie Kohn, 3 Tim Fairbrother, 2 Joe Gray, 1 Joe Marler.
Replacements: 16 Chris Brooker, 17 Mark Lambert, 18 James Johnston, 19 Charlie Matthews, 20 Luke Wallace, 21 Richard Bolt, 22 Rory Clegg, 23 Sam Smith.
Northampton: 15 Greig Tonks, 14 Tom May, 13 Jon Clarke, 12 James Downey, 11 Noah Cato, 10 Stephen Myler, 9 Martin Roberts, 8 Phil Dowson (c), 7 Ben Nutley, 6 Calum Clark, 5 Christian Day, 4 Samu Manoa, 3 Brian Mujati, 2 Andy Long, 1 Alex Waller.
Replacements: 16 Mike Haywood, 17 Paul Doran Jones, 18 Tom Mercey, 19 Mark Sorensen, 20 James Craig, 21 Stuart Commins, 22 Ryan Lamb, 23 Scott Armstrong.