Saracens flyhalf Owen Farrell scored all of his side's points to condemn Harlequins to their first Premeirship defeat this season.
While Farrell flourished at the Stoop hitting six from six, his opposite number Nick Evans showed cracks in his game only converting four of his eight goal-kicks.
Two weeks ago Farrell missed four of his five kicks at goal against Leicester Tigers at Wembley, and was hauled off for Charlie Hodgson.
But his perfect form did for Quins, who on top of Evans' 11 points scored a try through scrumhalf Danny Care.
Quins started off at their ambitious best, captain Chris Robshaw setting the standard with a superb slip pass to No.8 Nick Easter as they made steady progress towards Saracens' 22.
The visitors infringed at the ruck and Evans had his first shot at the posts which he calmly slotted for a 3-0 lead.
His opposite man Farrell also got his account under way by hitting a penalty from in front of the posts when Quins were penalised for offside.
Saracens prop Rhys Gill then fell foul of referee Andrew Small - adjudged offside - and Evans restored Quins' lead from the left side of the pitch.
On 21 minutes, Farrell levelled things up with his second successful attempt on goal and things seemed to be going the way of the hosts when Quins lock Olly Kohn was sent to the sin bin on 32 minutes for preventing Richard Wigglesworth from advancing after a tap penalty.
Farrell knocked over the follow up penalty but their lead was short-lived as three minutes later Care ducked under the attempted tackle of Petrus du Plessis and ran in a try from the 22.
The scrumhalf was fortunate that referee Small was unsighted to his apparent fumble in the ruck beforehand but nevertheless Evans converted for a 13-9 half-time lead.
In the second half the game broke up and it was Saracens who benefited the most.
Matt Hopper jinked out of trouble inside his half but was turned over and Farrell shaved Quins' lead by three.
Both team's hookers then came to the fore with Schalk Brits bursting out of Kohn's tackle and running right up the centre of the field before kicking on for Ashton to chase.
While the bounce beat both the England wing and Brown, Quins' replacement No. 2 Rob Buchanan covered half the pitch to sweep up for his fullback and prevent a score.
Buchanan then played his part in getting a nudge on in the scrum which earnt a penalty, yet Evans for the second time in the match, missed his mark.
Farrell however was smack bang in form and when Saracens' pack won a penalty from a maul he kicked his fifth of the day.
The rugby gods were conspiring against Evans and as he lined up another penalty the ball fell off his tee and the New Zealander was forced to rush his kick and subsequently missed.
Sarries replacement George Kruis was then sin binned for not releasing and Evans made no mistake to re-take the lead 16-15.
Yet Evans was clearly out of sorts and missed his next chance on goal and then hit an up and under which went back over his head and Brown was penalised for offside.
Farrell capitalised with his sixth goal kick to put Saracens back in the lead and they would not relinquish it.
Pens: Evans 3
Pens: Farrell 6
Harlequins: 15 Mike Brown, 14 Seb Stegmann, 13 Matt Hopper, 12 Jordan Turner-Hall, 11 Ugo Monye, 10 Nick Evans, 9 Danny Care, 8 Nick Easter, 7 Chris Robshaw, 6 Tom Guest, 5 George Robson, 4 Olly Kohn, 3 James Johnston, 2 Joe Gray, 1 Joe Marler.
Replacements: 16 Rob Buchanan, 17 Mark Lambert, 18 Will Collier, 19 Charlie Matthews, 20 Maurie Fa'asavalu, 21 Karl Dickson, 22 Rory Clegg, 23 Ollie Lindsay-Hague.
Saracens: 15 Alex Goode, 14 Chris Ashton, 13 Joel Tomkins, 12 Brad Barritt, 11 Chris Wyles, 10 Owen Farrell, 9 Richard Wigglesworth, 8 Ernst Joubert, 7 Will Fraser, 6 Kelly Brown, 5 Alistair Hargreaves, 4 Steve Borthwick (captain), 3 Petrus du Plessis, 2 Schalk Brits, 1 Rhys Gill.
Replacements: 16 John Smit, 17 Mako Vunipola, 18 Matt Stevens, 19 George Kruis, 20 Andy Saull, 21 Ben Spencer, 22 Charlie Hodgson, 23 David Strettle.
Referee: Andrew Small
Assistant referees: Ashley Rowden, Andrew Pearce
TMO: David Grashoff
Gloucester 31-25 London Welsh
England hopeful Freddie Burns sealed his side's 31-25 victory with a touchline conversion as Gloucester left it late to deny new boys London Welsh a third consecutive Premiership victory.
Burns' 73-minute effort capped a busy afternoon that saw him kick 16 points and receive a yellow card as he went head-to-head with former-Scotland flyhalf Gordon Ross - who notched 20 points of his own.
Going in 18-9 down at half-time Exiles head coach Lyn Jones must have been pleased with his side's response - and their resilience in the face of a good Gloucester side - to earn a losing bonus point.
But Gloucester deserved the win despite showing little of their trademark attacking flair in the absence of the injured Charlie Sharples and late withdrawal of Jonny May.
For London Welsh:
Pens: Ross 6
Tries: Monahan, Savage, Knight
Cons: Burns 2
Pens: Burns 3, Twelvetrees
London Welsh: 15 Seb Jewell, 14 Tom Arscott, 13 Sonny Parker, 12 Hudson Tonga'uiha, 11 Nick Scott, 10 Gordon Ross, 9 Tyson Keats, 8 Ed Jackson, 7 Michael Hills, 6 Daniel Browne, 5 Matt Corker, 4 Jonathan Mills (captain), 3 Paulica Ion, 2 Neil Briggs, 1 Frank Montanella.
Replacements: 16 Dan George, 17 Tom Bristow, 18 Arthur Joly, 19 Kirill Kulemin, Alfie To'oala, 21 Nick Runciman, 22 Ryan Davis, 23 Phil MacKenzie.
Gloucester: 15 Rob Cook, 14 Shane Monahan, 13 Mike Tindall, 12 Billy Twelvetrees, 11 James Simpson-Daniel, 10 Freddie Burns, 9 Dan Robson, 8 Sione Kalamafoni, 7 Akapusi Qera, 6 Peter Buxton, 5 Jim Hamilton (captain), 4 Tom Savage, 3 Rupert Harden, 2 Tommaso d'Apice, 1 Nick Wood.
Replacements: 16 Koree Britton, 17 Dan Murphy, 18 Shaun Knight, 19 Will James, 20 Gareth Evans, 21 Dave Lewis, 22 Henry Trinder, 23 Martyn Thomas.
Referee: Llyr Apgeraint-Roberts
Assistant referees: Peter Huckle, Kevin Stewart