Saints thoroughly deserved their victory, with fly-half Ryan Lamb kicking 13 points and Ben Foden and Roger Wilson scoring tries, while Harlequins were left rueing the absence of first choice fly-half Nick Evans and the number eight Nick Easter being sin-binned in the first half.
Saints piled up a decisive 11-point lead with Easter in the sin bin, and Evans’s replacement Rory Clegg missed two kickable penalties early in the second half just as Quins looked like mounting a comeback.
The defeat was only the second of Harlequins’ season and they remain on top of the Premiership table, while the victory means Saints stay third, four points behind second-placed Saracens, who host Bath tomorrow.
NORTHAMPTON: Foden, Ashton, Pisi, Downey, Cato, Lamb, Dickson, Tonga’uiha, Hartley, Doran-Jones, Manoa, Sorenson, Dowson, Wood, Wilson.
Replacements: May for Downey (72), Myler for Lamb (73), Roberts for Dickson (64), A. Waller for Tonga’uiha (64), Haywood for Hartley (72), Mujati for Doran-Jones (51), Day for Sorenson (69), Nutley for Wood (69).
HARLEQUINS: Brown, Williams, Hooper, Turner-Hall, Monye, Clegg, Care, Marler, Brooker, Johnston, Kohn, Robson, Robshaw, Wallace, Easter.
Replacements: S. Smith for Williams (50), Urdapilleta for Clegg (63), Lambert for Marler (57), Gray for Brooker (40), Fairbrother for Johnston (69), Vallejos for Kohn (60), Bolt for Robson (78), Guest for Wallace (50).
Referee: Dave Pearson (RFU).