Northampton fly-half Stephen Myler's try and boot steered the visitors to a 20-15 Premiership win over Saracens at Allianz Park.
The loss for Saracens was only their sixth at home in three and a half years, and also gives Exeter Chiefs the chance to go top on Sunday.
Northampton's tries from half-backs Stephen Myler and Lee Dixon were crucial, with Saracens only able to gain points from the tee.
With England head coach Eddie Jones watching on, Courtney Lawes was forced off during the first half after sustaining an ankle injury under the tackle of Hayden Smith.
Saracens dominated the lion's share of possession in the early stages of the tie, with forwards Richard Barrington and Jamie George looking the most likely to break through a resilient Northampton defence.
It wasn't until the 17th minute that Sarries took the lead, as scrum-half Ben Spencer slotted the first penalty, before doubling their lead soon after. The home side continued to press Northampton deep in to their own half, but it was Northampton who scored the game's first try after Jamie Gibson charged down Spencer's box kick, allowing Tom Wood to capitalise before finding Myler to crash over the line.
The fly-half then converted his own try, taking Saints in to a 7-6 lead. Spencer then handed kicking duties over to full-back Alex Goode, who added three more points from distance.
In the opening stages of the second half, Saints' scrum-half Dixon was able to find a gap in the Sarries defence to dive for the line, as he touched down at arms length despite the best efforts of Spencer. Myler added the extras, taking the visitors in to a 9-14 lead. Northampton then looked to capitalise once more, after great movement from Luther Burrell allowed him to find Ben Foden on the left wing, who leapt for the corner but knocked on under the tackle of Michael Rhodes.
A quick exchange of kicks saw Spencer bring Saracens within two points, before Myler restored the five point lead and Goode cancelled it out once more, bringing the score to 15-17.
The final score came from the boot of Myler, making the score 15-20 at Allianz Park. The game finished with Nils Mordt clearing in to touch, to the bemusement of his team-mates after having the opportunity for one more attack.
Pens: Spencer 3, Goode 2
Yellow Card: Spencer
Tries: Myler, Dickson
Cons: Myler 2
Pens: Myler 2
Saracens: 15 Alex Goode, 14 Mike Ellery, 13 Duncan Taylor, 12 Brad Barritt (c), 11 Chris Wyles, 10 Nils Mordt, 9 Ben Spencer, 8 Jackson Wray, 7 Kelly Brown, 6 Michael Rhodes, 5 Jim Hamilton, 4 Hayden Smith, 3 Petrus Du Plessis, 2 Jamie George, 1 Richard Barrington
Replacements: 16 Jared Saunders, 17 Hayden Thompson-Stringer, 18 Juan Figallo, 19 Alistair Hargreaves, 20 Jacques Burger, 21 Neil De Kock, 22 Marcelo Bosch, 23 Nathan Earle
Northampton: 15 Ben Foden, 14 Ken Pisi, 13 George Pisi, 12 Luther Burrell, 11 Tom Collins, 10 Stephen Myler, 9 Lee Dickson (c), 8 Teimana Harrison, 7 Tom Wood, 6 Jamie Gibson, 5 Victor Matfield, 4 Courtney Lawes, 3 Kieran Brookes, 2 Mikey Haywood, 1 Alex Waller
Replacements: 16 Reece Marshall, 17 Ethan Waller, 18 Paul Hill, 19 James Craig, 20 Sam Dickinson, 21 Tom Kessell, 22 JJ Harrahan, 23 Harry Mallinder
Referee: Thomas Foley
Assistant Referees: Roy Maybank, Andy Watson
TMO: Rowan Kitt