|Wasps (17) 22|
|Try: Willis, Kibirige, Young Con: Umaga 2 Pen: Umaga|
|Harlequins (14) 28|
|Try; Chisholm, Sinckler, Smith, Elia Con: Smith 4|
Harlequins produced an incredible comeback from 17-0 down to beat Wasps with a bonus point at the Ricoh Arena.
Jack Willis and Zach Kibirige put Wasps into a comfortable first-half lead but Quins hit back with tries from James Chisholm and Kyle Sinckler.
Marcus Smith's try then put Quins ahead for the first time before Elia Elia's score appeared to seal victory.
But, after Thomas Young gave Wasps hope, a TMO decision with three minutes left denied Wasps a match-winning try.
It consigned Dai Young's side to a fifth league defeat of the season but this was by far the most extraordinary after building up a healthy lead after early tries for flanker Willis and winger Kibirige, who was sent in by captain Joe Launchbury on his first appearance of the season.
Harlequins then sprang into life and a sweeping move was finished by Chisholm before England prop Sinckler charged over to reduce the deficit to three at the break.
Ten minutes into the second half, returning half-backs Danny Care and Smith combined to send the fly-half into the corner and then hooker Elia scored from a five-metre line-out to put Quins 11 points up.
But Wasps rallied and a catch-and-drive saw Young score to get within range.
After prop Joe Marler was sin-binned for Quins, Jimmy Gopperth's break led to another line-out in the corner.
Wasps drove for the line again and a bumper festive crowd thought the hosts were about to steal the game, only for Elia to rip the ball from the maul and allow Quins to survive and claim a third win of the season.
Wasps director of rugby Dai Young told BBC Coventry and Warwickshire:
"The first 30 minutes we were excellent, dominant in all facets of the game, really physical and 17 points up, you have to think you'll take the game home.
"They scored a soft try and then the intensity went out of our game and we lost momentum, field position and it took until the last 15 minutes to get it back.
"We made one or two errors, the belief drained from us and our heads dropped far too easily until the last part of the game."
Harlequins director of rugby Paul Gustard:
"In the first quarter we were extremely poor as we regularly lost possession and dropped off tackles to concede 17 soft points.
"For the next 40 minutes, it was one-way traffic as our set-piece was on top throughout but then the final eight or nine minutes saw us nearly manage to grab defeat from the jaws of victory.
"I thought our back row were excellent as last week at Ulster we were bullied, and Marcus Smith kicked well to give us field position. To come away with a bonus-point win is a good leg up for the team."
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Wasps: Minozzi; Kibirige, Fekitoa, Le Bourgeois, Watson; Umaga, Robson; Harris, Taylor, Brookes, Launchbury (c), Matthews, Willis, Young, Vailanu,
Replacements: Cruse, West, Owlett, Cardall, Carr, Porter, Gopperth, de Jongh
Harlequins: Chisholm; Murley, Campagnaro, Lang, Ibitoye; Smith, Care; Marler, Elia, Sinckler, Lewies, Symons, Chisholm, Robshaw (c), Lawday
Replacements: Musk, Garcia Botta, Collier, Cavubati, Dombrandt, Landajo, Lasike, Goneva