|Wasps (10) 16|
|Try: Simpson Con: Goode Pens: Goode 3|
|Harlequins (13) 23|
|Tries: Matthews, Penalty Cons: Evans 2 Pens: Evans 3|
Harlequins edged ahead of Leinster at the top of Pool Two as they ended the long-running series of London derbies against Wasps with an away victory in the European Champions Cup.
Quins led 6-3 after 20 minutes before Coventry-bound Wasps hit back courtesy of an electric solo Joe Simpson try.
But lock Charlie Matthews galloped over to make it 13-10 to Quins at half-time.
Two Andy Goode penalties to one from Nick Evans levelled matters, but a penalty try gave the visitors the win.
Wasps - who were missing captain James Haskell after a virus - and Harlequins have been playing this London derby since the 19th century.
But with the imminent departure of Sunday's hosts to their new home in Coventry, this was a suitably competitive final chapter to their history as warring neighbours.
A tight affair was always on the cards, with three of their past five Premiership matches decided by one point, and the others by just two and three.
And this game was nip and tuck until the final 20 minutes when the Harlequins pack assumed total dominance in the scrums and laid the platform for the visitors to make it two wins out of two in Europe this season.
A penalty duel between respective fly-halves Evans and Goode saw Quins lead 6-3 quarter of the way through the game before the 6ft 8in, 18-stone Matthews - hard to ignore at the best of times - took centre stage.
He was narrowly denied a try when he was held up over the line but he could not keep out of the game, although his next involvement was less welcome for the visitors.
Wasps scrum-half Simpson, who seems to have slipped down the England pecking order, ripped the ball from Luke Wallace and beat the gangly Matthews before racing clear of the despairing dive of Chris Robshaw to score a cracking try.
However, Matthews redeemed himself on the stroke of half-time, finishing off a fine move after a superb break by mobile hooker Dave Ward and some magical handing involving the likes of England full-back Mike Brown and Fiji wing Asaeli Tikoirotuma.
With both tries converted the visitors led by three points at half-time but a further kicking duel between Goode and Evans meant the sides were locked together at 16-16 on the hour.
The scores may have been level but Quins were looking the stronger side and their pack upped the power in the scrums, duly winning a penalty try to secure the decisive score.
Wasps boss Dai Young:
"We were never in control from the word go, Quins were by far the better team and the final score-line flattered us.
"We lacked energy and it was a really flat performance from a very tired team.
"We've had some big performances this season but that caught up with us today and it was a reality check."
Quins boss Conor O'Shea:
"We should have taken more chances than we did but I'm delighted as it takes a good side to do that to Wasps here at Adams Park.
"It was a big step forward as it was a hugely physical performance from us as people say we can't win against sides that are physical against us.
"Our leading players face a huge four weeks with England and with the LV= Cup coming up it's a chance to give the legs of Nick Easter and Nick Evans a rest."
Wasps: Masi; Wade, Daly, Leiua, Varndell; Goode, Simpson; Mullan, Festuccia, Cittadini, Launchbury, B Davies, Johnson, Jones, Hughes.
Replacements: Gaskell for Davies (57), Lindsay on for Festuica (63), McIntyre for Mullan (65), Swainston on for Cittadini (65), Young on for Johnson (65) C Bell for Leiua (72), Miller for Goode (68),
Not Used: C Davies.
Harlequins: Brown; Yarde, Hopper, Lowe, Tikoirotuma; Evans, Care; Lambert, Ward, Sinckler, Matthews, Robson, Wallace, Robshaw, Easter.
Replacements: Collier for Sinckler (56), Marfo for Lambert (73), Buchanan for Ward (73).
Not Used: Twomey, Trayfoot, Dickson, Turner-Hall, Lindsay-Hague.
Ref: Marius Mitrea (Italy).