In running four tries past Saracens, the Saints ensured they headed to next Sunday's LV= Cup final against Gloucester in great style.
Conditions at the Gardens were perfect for running rugby, as demonstrated several times during the first 10 minutes when the hosts kept the ball in hand, notably with a superb Roger Wilson break up the right wing. Saracens, on the other hand, showed their intent right from the kick off when Derick Hougaard attempted a drop goal from halfway.
The South African tried another after 13 minutes from even further out - just one of six shots at goal of one sort or another he had in the first 20 minutes - and his accuracy meant that Saracens got the first points on the board and indeed a lead at the end of the opening quarter, even though they were nevertheless already behind on the try count.
Wilson's run had set up excellent territory deep in Saracens territory. Turning on the power at scrum time brought a penalty advantage, which the Saints used to good effect, Phil Dowson powering over on the left. Geraghty missed the conversion, but his next shot, a 22nd-minute penalty, both took his team back to within a point and immediately punished Ernst Joubert's yellow card.
Saracens' skipper had seen yellow for a professional foul but without him his team mates created their best try opportunity of the match so far just before the half-hour. Ironically enough for their reputation, Saracens showed how dangerous they could be when they put their mind to it, Schalk Brits taking a Bruce Reihana bomb superbly and setting Neil De Kock away down the left wing. His chip took out the covering defenders and the scrum-half was only beaten by the bounce of the ball.
However the visitors still extended their lead with a fourth Hougaard success, but they immediately spoiled their good work by conceding a penalty right in front of the sticks for Geraghty to pull three points back.
With Joubert's comeback to the action came a return to form, Hougaard trying a third drop-goal. Like its predecessors it was off target and although it looked like Hougaard would be reprieved when Geraghty missed a 39th-minute penalty Saracens still went into the break behind.
Two moments of ill discipline were Saracens' undoing, firstly a penalty on halfway that Lee Dickson took full advantage of with a quick tap and go, and then one just outside the 22 that not just allowed Geraghty to land his third three-pointer but also ensured that Saracens would have 14 men for the opening 10 minutes of the second half thanks to Richard Skuse's yellow card.
There were two further blows for the visitors in the opening minutes of the second half, firstly with Brits - who had been limping before the break - being replaced by Ethienne Reynecke, and then Chris Wyles coming off with a leg injury.
Nevertheless where the blows count most is on the score board, and before Saracens were back to their full compliment they were 10 points further behind thanks to two fantastic tries.
First over the line was Brian Mujati, who beat a desperate tackle and the dead ball line to ground in the right corner. Then Diggin finished off a sublime move that had the Gardens faithful on their feet. Geraghty's offload was sublime, as was Chris Ashton's supporting running line. And though the Guinness Premiership's leading try scorer could have lit the afterburners he instead chose to draw the final man and put his wing partner over unopposed.
Unfortunately Geraghty's accuracy from the tee was off not just with the conversions but also a close range penalty that came back off the bar. This meant that Saracens were still in the contest with a quarter of the match to go, and with Kiwi pair Justin Marshall and Glen Jackson on the field some new hands on the tiller.
Jackson was almost immediately on the score sheet with his team's fifth penalty, but it proved to be a mere blip on the one-way train that was the second half scoring sequence.
Saints finally put the contest to bed with 10 minutes to go when they ruthlessly punished a poor Marshall box kick. The scrum-half missed touch, which allowed his fellow former All Black Reihana to run it back with interest, and although Saracens covered manfully they couldn't stop Neil Best powering over.
Geraghty's conversion took the Saints past 30 points, and although Justin Melck scored a try - and both teams ended the game a man down thanks to a spot of handbags between Juandre Kruger and Mouritz Botha - it was just a consolation for the Men in Black as they watched the Saints march into the final.
Teams:
Northampton Saints - Reihana; Ashton, Clarke, Downey (Myler 71mins), Diggin; Geraghty, Dickson (Dickens 66mins; Tonga'uiha (Dreyer 71mins), Sharman (Long 71mins), Mujati, Fernandez Lobbe (Cannon 71mins), Kruger, Dowson (capt)(Easter 71mins), Best, Wilson
Scorers - Tries: Dowson, Mujati, Diggin, Best; Con: Geraghty; Pens: Geraghty (3)
Yellow card - Dreyer (73mins), Kruger (75mins)
Saracens - Goode; Penney, Ratuvou, Barritt, Wyles (Haughton 42mins); Hougaard (Jackson 50mins), De Kock (Marshall 50mins); Lealamanua (Mercey 11mins (Brown 63mins)), Brits (Reynecke 40mins), Skuse, Smith (Ryder 53mins), Botha, Burger, Saull (Brown 43-50mins, Melck 53mins), Joubert (capt)
Scorers - Try: Melck; Pens: Hougaard (4), Jackson
Yellow cards - Joubert (21mins), Skuse (40mins), Botha (75mins)
Lv+ Cup man of the match - Soane Tonga'uiha
Referee - Romain Poite (FFR)
TIMELINE:
1min SAR Miss DG Hougaard
4mins SAR Pen Hougaard 0-3
8mins SAINTS Try Dowson 5-3
12mins SAR Miss pen Hougaard
13mins SAR Miss DG Hougaard
15mins SAR Pen Hougaard 5-6
19mins SAR Pen Hougaard 5-9
21mins SAR Yellow card Joubert
22mins SAINTS Pen Geraghty 8-9
29mins SAR Pen Hougaard 8-12
30mins SAINTS Pen Geraghty 11-12
33mins SAR Miss DG Hougaard
39mins SAINTS Miss pen Geraghty
40mins SAR Yellow card Skuse
40mins SAINTS Pen Geraghty 14-12
HALF-TIME SAINTS 14 SARACENS 12
46mins SAINTS Try Mujati 19-12
48mins SAINTS Try Diggin 24-12
55mins SAINTS Miss pen Geraghty
60mins SAR Pen Jackson 24-15
70mins SAINTS Try Best Con Geraghty 31-15
73mins SAINTS Yellow card Dreyer
75mins SAINTS Yellow card Kruger
75mins SAR Yellow card Botha
75mins SAR Try Melck 31-20
FULL-TIME SAINTS 31 SARACENS 20