Derick Hougaard sank Northampton with a 24-point man-of-the-match performance that hauled his team into the top half of the Aviva Premiership Rugby table.
Despite an impressive start Northampton's indiscipline proved costly at Vicarage Road as referee David Pearson punished them with a series of penalties and Hougaard filled his boots. Paul Diggin scored the game's only try in the last minute, crossing from the right to secure the visitors a losers' bonus.
Saints began the day as the league's only unbeaten team, seeking to recapture the top spot they had lost overnight to London Irish. But they were without England duo Chris Ashton and Courtney Laws, both rested as part of the agreement between the Aviva Premiership Rugby clubs and the RFU which ensures Elite Player Squad members are not overplayed.
The visitors started the sharper and were ahead inside five minutes following a penalty by Shane Geraghty, awarded for a scrum offence. Hougaard equalised from an eighth-minute penalty after Saints went offside in a ruck, but a clever kick-through by Geraghty should have led to a try for the visitors, only for Christian Day to fumble on the line.
Saracens were penalised for offside in front of their posts, and Geraghty kicked Northampton back into the lead and wasted a chance to increase it after 16 minutes when he hooked a penalty for a scrum collapse wide of the near post.
Saracens had another let-off in the 18th minute when Brad Barritt's attempted kick-through rebounded off a group of opponents and led to a straight chase for the line between Neil de Kock and Tom Wood. Pearson consulted assistant referee Roy Maybank before agreeing that the Sarries scrum-half was first to the ball after it had crossed their line.
Northampton were giving their hosts a torrid time in the scrum where loosehead Deon Carstens was repeatedly penalised for not binding correctly. Geraghty extended Northampton's lead to six points after 22 minutes when another scrum nosedived into the pitch but Northampton drifted offside and Pearson presented Hougaard with the opportunity to cut the deficit from 35 yards.
An early turning point came shortly afterwards when Hougaard took aim from 45 yards before firing an impressive drop-goal high between the posts to level the scores with a goal which had a galvanising effect on Saracens.
The hosts drove upfield, forcing Northampton to concede two penalties in quick succession. The first saw the home team continue to play advantage, so when Calum Clark promptly conceded a second penalty by trying to interfere with the drive Pearson sent him to the sin-bin as Hougaard kicked his fourth goal.
Another Hougaard goal six minutes from the break turned the game on its head as Northampton struggled with 14 men. Yet it was the visitors who finished the half as they began, with Geraghty's penalty 90 seconds from the interval giving them a 15-12 lead.
Referee Pearson awarded Saracens a penalty two minutes after the restart as Saints went offside in front of their posts in an attempt at desperate defence. Hougaard took advantage with goal number five. Home pressure was rewarded in the 53rd minute when Northampton tried to halt an attack illegally, and Hougaard did brilliantly to kick a difficult goal for a right-footed player from wide out on the right wing.
Saracens now drove upfield at every opportunity, sucking in defenders, and one turned out to be fly-half Geraghty who not only got on the wrong side of a ruck in front of his posts, he failed to get clear fast enough to satisfy Pearson, who sent him to the bin in the 58th minute.
Hougaard kicked his eighth goal, before Diggin crossed for the visitors at the end.