Saints held a 20-11 half-time lead after tries from England stars Ben Cohen, who powered his way over, and Matt Dawson, who found a gap in the defence after a sustained period of pressure, and conversions from former Test No.10 Paul Grayson.
Saracens' half-time deficit could have been a bit worse had French utility back Thomas Castaignède not profited from a shocking pass from Dawson. Castaignède, playing at fullback, ran the full length of the field for the try, but Goode was unable to add the conversion.
A points-scoring blitz between minutes 59 and 64 saw a 14-point haul for Saints, which knocked the stuffing out of the visitors.
Scotland and Lions prop Tom Smith touched down in the 59th minute before No.8 Grant Seely got in for his team's fourth try in the 64th. Grayson converted both scores to put the home team ahead by 34-11 with just over 15 minutes remaining.
Saracens added some respectability to the scoreboard with tries from their No.8 Kris Chesney and fly-half Andy Goode, who had opened the scoring in the fourth minute, but it was too little too late by then.
Saracens are into six position on the Zurich Premiership standings (they have a better points difference than Wasps, who play London Irish on Sunday), while Northampton remain in sixth place, although they now lead Sarries by nine points.
For Northampton:Tries: Cohen, Dawson, Smith, SeelyCons: Grayson 4Pen: Grayson 2
For Saracens:Tries: Castaignède, Chesney, GoodeCons: Goode 2Pens: Goode 2