Despite pre-match talk, the encounter failed to produce many sparks
Saracens ended Northampton's unbeaten record at a rain-soaked Vicarage Road, with fly-half Derick Hougaard the home side's goal-kicking hero.
Tom Wood's charge-down of a clearance by Hougaard was the only try chance for either side in the first half.
Hougaard's drop-goal and four penalties to three penalties by Shane Geraghty gave Sarries a 15-12 half-time lead.
Hougaard kept up his 100% kicking rate after the break, but Paul Diggin's late try earned Saints a losing bonus point.
Despite all the pre-match talk of the intensity of the teams' rivalry and the potential for fireworks, the first half was a relatively tame affair - no doubt at least partly a result of the steady rain.
Northampton began the brighter, having the territorial advantage, but could only come up with two Geraghty penalties, although the fly-half missed another fairly straight-forward kick.
Hougaard had also notched one for the home side before the first real try-scoring chance of the match.
Wood blocked Hougaard's attempted kick and hacked the ball towards the try-line, but was just beaten to the ball by Saracens scrum-half Neil de Kock.
Having just saved his side from conceding a try, De Kock then handed Saracens an opportunity as his kick was charged down by Calum Clark, and they were lucky to escape with just conceding a five-metre scrum.
Deon Carstens was penalised for bringing it down, allowing Geraghty to notch his third penalty, which was instantly cancelled out by another from Hougaard.
The fly-half added two more penalties and an audacious drop-goal from near the half-way line to send the home side in six points ahead at the break.
Despite the rain finally stopping at half-time, there was no obvious increase in the amount of running rugby, the only change to the scoreline coming from three more Hougaard penalties.
With the game edging further away from Northampton, Geraghty was harshly yellow-carded for failing to roll away after making a tackle, but oddly this seemed to inspire his side.
They finally had a try-scoring opportunity as Joe Ansbro's break set up a great three-on-one chance just yards from the line.
But captain Dylan Hartley wasted the chance, opting to go himself rather than offloading to either of the supporting players.
Having finally got sight of the Saracens try-line, Northampton seemed revitalised, and stayed camped in opposition territory for the remainder of the game.
It eventually paid dividends in the final minute when Diggin went over from close range in the right-hand corner to ensure that despite losing their unbeaten record, they would at least leave Vicarage Road with a bonus point.
Saracens rugby director Brendan Venter:
"We did not show tactical sharpness in the opening 20 minutes, but I told the guys to take the Treviso game off the shelf, the kicking game that we used for that European game last season.
"We had trouble in the scrum at first, but the pack turned it for us against a very strong Northampton pack who have destroyed everyone ahead of them so far.
"We studied (referee) Dave Pearson's games so far and he does the same in every game, fair penalty awards and spread across the game. He is consistent and very, very impressive.
"And never underestimate how important it is for us to have a fit and available Steve Borthwick in the team in terms of both his tactical brain and leadership qualities."
Northampton rugby director Jim Mallinder:
"We think Dave Pearson had a disappointing game. When you lose you tend to look at the referee more critically, but we'll look closely at the video before saying anything further.
"I do believe the two sin-binnings were harsh. Calum Clark just went in to make a tackle and Shane Geraghty also made a tackle and tried to roll away quickly. A penalty, yes, but hardly a yellow card. These sin-binnings are very important.
"But you need to control the ball to control the game and we didn't during the middle of the game."
Saracens: Mordt, Strettle, Ratuvou, Barrett, Wyles, Hougaard, de Kock, Carstens, Reynecke, Nieto, Borthwick, Botha, K. Brown, Burger, Joubert. Replacements: Tagicakibau for Mordt (41), Wigglesworth for de Kock (51), Parr for Carstens (75), Brits for Reynecke (41), Du Plessis for Nieto (51), Smith for Botha (66).
Not Used: Barrell, Farrell.
Northampton: Foden, Diggin, Ansbro, Downey, Reihana, Geraghty, Dickson, Tonga'uiha, Hartley, Mujati, Sorenson, Day, Clark, Wood, Dowson. Replacements: Clarke for Ansbro (73), Myler for Geraghty (68), Wilson for Sorenson (62), Easter for Wood (73).
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