Saints started brightly, earning a long-range penalty for Stephen Myler to find his range. Myler missed, but three minutes later he had another chance to open his account.
Dylan Hartley intercepted an ambitious Joel Tomkins off-load to spark a cracking counter-attack which involved plenty of accuracy and pace from both forwards and backs. Eventually a penalty came, but the wind proved tricky to overcome from closer range, too, with Myler hooking this attempt to the left.
It was therefore little surprise when Myler pushed the next penalty - awarded on the 10-metre line - to the sidelines. But Saracens proved up to the challenge posed by the Saints maul, pushing back the initial drive and then forcing a penalty in the next phase of play.
Saints had had the better of the opening 10 minutes, looking to create opportunities with ball in hand and forcing Saracens back with some aggressive defence. But the first lucky bounce of the ball - quite literally - went the hosts' way when a James Wilson clearance kick from just outside his 22 headed straight over the dead ball line some 80 metres away.
But re-sets one, two and three all held, and when Jamie Elliott stopped Tomkins in his tracks to force the England tourist to hold onto the ball, that initial danger had been cleared.
Saracens were soon back in the danger zone, however, and while they looked threatening at times Saints' rearguard restricted them to an Owen Farrell grubber that bounced harmlessly out of play.
Although there had been plenty of attacking intent shown by both sides the physicality in defence had also been holding sway. But inside three minutes at the end of the opening quarter Saints blew the game wide open.
First to score was Brian Mujati, whose right arm sneaked out of the bottom of a ruck to get the ball over the whitewash.
Television Match Official Graham Hughes took plenty of time to make the decision, but while this got the travelling thousands into good voice it was nothing compared to what was to follow.
Saracens got the ball back from the kick off and looked to create some space, but Samu Manoa levelled Chris Ashton, Lee Dickson disrupted the breakdown, thereby creating an opening for Soane Tonga'uiha to snatch the turnover. Hartley and Christian Day were both in support, but with just Steve Borthwick there to cover there was plenty of space for Elliott to exploit, which he duly did.
Myler added both conversions, and a subsequent penalty, and all of a sudden Saints had a 17-0 lead.
That's not to say that Saracens did not have their chances. Mako Vunipola had a couple of barrelling runs, and Kelly Brown nicked a turnover to take play into the visitors' 22. They also got a kickable penalty when Tom Wood failed to roll away after taking Schalk Brits man and ball.
But Farrell, like Myler before him, found the wind too tough an opponent, which meant that the players headed into the changing rooms with Saints still leading by the same 17 points.
By the end of the first half the rain was teeming down onto North London, and for all the stability in the set piece the artificial surface was proving as slippy as any pitch in the rain.
Ashton had gone over late in the first half, as did Vunipola at the start of the second, but when David Strettle broke clear later in the same attack a try looked a formality. Wilson and Ben Foden had other ideas, pulling off a brilliant double tackle, and when the forwards followed this up by winning a penalty at the subsequent five-metre scrum, and another on the next put-in it looked like they had weathered that early storm.
But Saints were struggling to maintain steady possession and get out of their own half, and when Farrell stepped up to get his team onto the scoreboard it was a deserved three points.
Three minutes later the score became 6-17, and with Saracens having upped their game in defence Saints were certainly finding things harder than they had before the break.
But then Dickson popped down the blindside to create a try for GJ Van Velze, and with another superb touchline conversion from Myler the half-time lead had actually increased by a point as the clock ticked into the final quarter.
It was a much-needed score, and when Saracens punished Elliott's yellow card by creating a try for Duncan Taylor the Allianz Park crowd was brought very much to life.
The home cheers were silenced eight minutes later as Myler landed another superb kick at goal, and as Saints held out the one final, desperate attack from Saracens the black, green and gold hordes took over to cheer their team to a date at Twickenham.
2mins SAINTS Miss pen Myler
5mins SAINTS Miss pen Myler
20mins SAINTS Try Mujati Con Myler 0-7
22mins SAINTS Try Elliott Con Myler 0-14
26mins SAINTS Pen Myler 0-17
38mins SARACENS Miss pen Farrell
HALF-TIME SARACENS 0 SAINTS 17
51mins SARACENS Pen Farrell 3-17
54mins SARACENS Pen Farrell 6-17
58mins SAINTS Try Van Velze Con Myler 6-24
60mins SAINTS Yellow card Elliott
64mins SARACENS Try Taylor Con Farrell 13-24
72mins SAINTS Pen Myler 13-27
FULL-TIME SARACENS 13 SAINTS 27