Owen Farrell's 76th minute penalty snatched victory for Saracens in what was a very evenly matched affair and in the process reduced Harlequins to their first loss of the 2012-13 season.
So evenly matched were the sides, the lead at any one time never increased beyond four points.
In an uncharacteristic performance from Nick Evans, the fly-half missed four of his eight attempts on goal. His counterpart, Owen Farrell had a 100% record with six penalties.
Despite being reduced to 14 men with a yellow card to Olly Kohn, Danny Care scored the game's only try minutes before half time, giving the quartered men a 13-9 lead.
Evans could only add one penalty in the second half as Farrell notched three to claim a 16-18 victory.
Saracens were effective in shutting Harlequins' expansive game down killing any offloading opportunity by double tackling Harlequins in attack.
Evans started the game brightly, giving his side an early 3-0 lead. He was then in charge of mastering two clever chip kicks through the Saracens defence for Ugo Monye and Care. Evans was unable to extend the lead through the boot and three minutes later, Farrell leveled the scoring.
Both kickers exchanged penalties before Mike Brown's defensive effort prevented a sure try. Schalk Brits broke through the Harlequins line and despite having numbers to his left infield, the hooker decided to pass to Chris Ashton on the wing. As the English winger charged down field, Brown tackled him into touch.
Harlequins were dealt a blow just beyond the half hour mark when Kohn was yellow carded for failing to retreat ten metres after a quick tap penalty from Richard Wigglesworth.
Despite being reduced to 14, Harlequins scored the game's only try through Care. Tom Guest made a half break to just outside the 22 metre line. With the ball available to Care and despite what looked to be a knock on, the scrum half made a darting run to score under the posts. With Evans' conversion Harlequins led 13-9.
In the early stages of the second half, Farrell added a penalty on 44 minutes, before Brits' sensational run almost led to a score. The expansive hooker broke through tackles from Kohn, Johnston and Care before putting in a chip kick, which any back would be proud of, to the on rushing Ashton.
In a foot race between Ashton and Brown, the Harlequins full-back did enough to disrupt the winger, the ball went loose and Rob Buchanan touched down to prevent the score.
Sandwiched between two Evans penalty misses was Farrell's fifth successful kick. Evans then missed his fourth kick of the afternoon with eight minutes remaining on the clock which would have extended Harlequins' lead.
After this miss, a wayward up and under caught by an offside Brown allowed Farrell to step up and kick the winning points for the visitors.
