Fullback Mike Brown scored the pick of the tries as Harlequins survived a concerted fightback by Wasps to secure their tenth successive Premiership victory on Sunday.
Brown crossed 10 minutes after the break in between centre Matt Hopper's seventh-minute touchdown and flank Luke Wallace's score as the leaders roared into a 22-6 lead with 57 minutes played at Adams Park.
But Hopper's departure for the sin-bin saw Hugo Southwell claim a first try for the home side and when England winger Tom Varndell followed suit nine minutes from time, the game was back in the balance.
However, flyhalf Nick Robinson twice hit a post as he failed to add to his six points, and opposite number Nick Evans' single penalty and two conversions helped to see the visitors home for their 14th consecutive win in all competitions.
It took Quins just seven minutes to get their noses in front, Hopper running on to prop Joe Marler's inside pass to touch down beneath the posts, with Evans adding the conversion.
Robinson reduced the deficit within two minutes with a well-struck penalty and scrumhalf Joe Simpson might have put Wasps ahead with when he broke through the cover and was grounded just short of the line by Hopper.
The Wasps flyhalf should have dragged the home side back to within a point, but saw his penalty attempt come back off the post with the visitors finding themselves camped deep inside their own half.
A dominant home pack was causing all kinds of problems for Quins in the set-pieces, but they had to wait until the final minute of the first half to win the penalty from which Robinson pulled them back to within a point.
However, the Quins tight five restored pride as they turned the tables on their hosts at a 44th-minute scrum to allow Evans to stretch their lead to 10-6 four minutes after the restart.
They eased further clear in stunning fashion with their second try of the game as quick hands from No.8 Chris Robshaw and Hopper gave the opportunity to Brown to chip over the top before winning the chase to touch down.
Quins cemented their lead seven minutes later when Wallace bludgeoned his way over from Danny Care's deft kick and Evans converted.
Hooper's afternoon took a turn for the worse when he was yellow-carded, and Wasps took advantage as Southwell touched down in the corner with 63 minutes gone.
Varndell made light of Hopper's return as he burst past him to run in his side's second try eight minutes later, although Robson hit the post for a second time with his conversion attempt to leave his side six points adrift.
Tries: Southwell, Varndell
Pens: Robinson 2
Tries: Hopper, Brown, Wallace
Cons: Evans 2
Wasps: 15 Hugo Southwell, 14 Tom Varndell, 13 Dominic Waldouck, 12 Riki Flutey, 11 Christian Wade, 10 Nick Robinson, 9 Joe Simpson, 8 John Hart (captain), 7 Matt Everard, 6 Richard Birkett, 5 Marco Wentzel, 4 Ed O'Donoghue, 3 Ben Broster, 2 Rob Webber, 1 Tim Payne.
Replacements: 16 Tom Lindsay, 17 Zak Taulafo, 18 Jeremy Castex, 19 Joe Burton, 20 Sam Jones, 21 Charlie Davies, 22 Ryan Davis, 23 Elliot Daly.
Harlequins: 15 Mike Brown, 14 Seb Stegmann, 13 Matt Hopper, 12 Tom Casson, 11 Sam Smith, 10 Nick Evans, 8 Chris Robshaw (captain), 7 Luke Wallace, 6 Maurie Fa'asavalu, 5 Charlie Matthews, 4 Tomas Vallejos, 3 James Johnston, 2 Joe Gray, 1 Joe Marler.
Replacements: 16 Chris Brooker, 17 Mark Lambert, 18 Kyle Sinckler, 19 Pete Browne, 20 Will Skinner, 21 Richard Bolt, 22 Ben Urdapilleta, 23 Ugo Monye.
Referee: Dean Richards
Saracens 15-11 London Irish
Owen Farrell kept Premiership champions Saracens on the coat-tails of leaders Harlequins by kicking all his side's points in a narrow victory over London Irish at Vicarage Road.
Irish took the lead through a Tom Homer kick but Farrell struck three times before the break to hand Sarries the advantage.
Daniel Bowden's penalty reduced the deficit before two more Farrell kicks made it 15-6. David Paice secured the Exiles a losing bonus point with the only try of the match, which Bowden failed to convert.
The match got off to a bad start for the hosts with wing Joe Maddock lost to a leg injury after just three minutes, David Strettle his replacement off the bench.
Homer fired Irish into the lead on five minutes with a penalty which Farrell cancelled out three minutes later.
Irish had the chance to regain the lead after lock Matt Garvey smashed through three tackles before being hauled down. Saracens then had hooker John Smit sin-binned for picking up the ball after it had emerged from the back of the resulting ruck, but Homer fired his subsequent penalty attempt wide.
This miss was a costly one, with Saracens taking the lead on 15 minutes courtesy of Farrell's second goal, before the 20-year-old added his third kick of the half when Irish were caught offside on 22 minutes.
Irish responded by laying siege to the hosts' line, winning a succession of scrums, but the Saracens defence stood firm.
The best chance for either side to bag a try in the opening period went to the hosts on the stroke of half-time, James Short going over after collecting Farrell's chip only for the video referee to rule he had failed to ground the ball under pressure from Bowden.
Irish went back on the offensive from the re-start with the impressive Garvey and Chris Hala'ufia again a threat with their powerful ball-carrying.
Irish were rewarded for their perseverance when Bowden drove a 49th-minute penalty between the posts.
Yet within minutes Irish were penalised for not releasing after Matt Stevens had won a scrum and set up an attack on the right, Farrell's 52nd-minute penalty restoring Saracens' six-point lead.
And Farrell made it five from five on 69 minutes, a 40-metre effort that left Irish requiring two scores to win.
They got the first on 76 minutes, the pack driving for the line and propelling Paice over for a try which Bowden failed to convert, but that was the end of the scoring.
Pens: Farrell 5
For London Irish:
Pens: Homer, Bowden
Saracens: 15 Alex Goode, 14 Joe Maddock, 13 Chris Wyles, 12 Adam Powell, 11 James Short, 10 Owen Farrell, 9 Ben Spencer, 8 Ernst Joubert, 7 Andy Saull, 6 Jackson Wray, 5 Mouritz Botha, 4 Steve Borthwick (captain), 3 Carlos Nieto, 2 John Smit, 1 Matt Stevens.
Replacements: 16 Jamie George, 17 Rhys Gill, 18 Petrus du Plessis, 19 George Kruis, 20 Kelly Brown, 21 Luke Baldwin, 22 Duncan Taylor, 23 David Strettle.
London Irish: 15 Tom Homer, 14 Topsy Ojo, 13 Joe Ansbro, 12 Jonathan Spratt, 11 Adam Thompstone, 10 Dan Bowden (captain), 9 Paul Hodgson, 8 Chris Hala'ufia 7 Jamie Gibson, 6 Declan Danaher, 5 Matt Garvey, 4 Nick Kennedy, 3 Paulica Ion, 2 James Buckland, 1 Alex Corbisiero.
Replacements: 16 David Paice, 17 Clarke Dermody, 18 Faan Rautenbach, 19 Bryn Evans, 20 Ofisa Treviranus, 21 Guy Armitage, 22 Adrian Jarvis, 23 Darren Allinson.
Referee: Andrew Small
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