Saracens (9) 15
Pens: Farrell 3, Hodgson 2
Wasps (13) 20
Tries: Wade, Varndell Cons: Robinson 2 Pens: Robinson 2
Tom Varndell's try proved the crucial score of the game
Premiership champions Saracens began the defence of their title with a defeat by Wasps that marks a first loss under director of rugby Mark McCall.
Both sides exchanged early penalties before Wasps' flying wing Christian Wade crossed for the opening try.
Wasps debutant fly-half Nick Robinson converted, adding a penalty to give them a fully-deserved half-time lead.
Charlie Hodgson added two penalties for Sarries after the break but Tom Varndell's score sealed Wasps' victory.
It was not a happy return to Twickenham for Saracens but the defeat makes them the ninth defending champions in 11 years to lose on the opening day.
It started well enough with Owen Farrell, the young hero of last season's final, firing over an early brace of penalties.
But Wasps, with five debutants taking the field, looked barely recognisable from the side that suffered a torrid campaign last season as Robinson got them on the scoreboard with the boot.
A sweeping move by Wasps put Wade away for his try after swift handling by Riki Flutey and Chris Bell.
Farrell and Robinson kicked another penalty apiece as Wasps held a slender lead at the break.
Sarries' young stand-off Farrell missed a shot at goal after the break and he was replaced on 50 minutes by Hodgson.
The England man soon brought his side to within one point and then gave them a 15-13 lead with his second shot at goal after Carlos Nieto's scrummaging earned a penalty.
But just as the champions were building momentum two missed tackles allowed Varndell to go in under the posts and make Robinson's conversion a certainty.
Hodgson had a late chance to reduce the arrears further but hooked his kick wide.
Wasps' new director of rugby Dai Young:
"The first thing I asked was for 100% commitment and they gave me that today.
"They showed clear intent to play attacking rugby and they did that. Sometimes they made wrong decisions, and our scrum was not right - but we overcame that.
"We played a lot of rugby, won the collisions and put them under a lot of pressure.
"Saracens had us in a stranglehold for a while, but our defence was good. It's one game, one win, nothing more, and it's Leicester next week."
Saracens director of rugby Mark McCall:
"We are normally very good at closing out tight games, so it was a bitter blow not to go on and win.
"But Wasps were more physical and gained far too many yards to put us on the back foot in the first half and towards the end, and we failed to get enough clean lineout balls."
Saracens: Goode; Strettle, Powell, Barritt, Short; Farrell, de Kock; Gill, Brits, Nieto, Borthwick, Botha, Melck, Saull, Joubert.
Replacements: George, Carstens, Du Plessis, Kruis, Wray, Spencer, Hodgson, Taylor.
Wasps: Southwell; Varndell, Bell, Flutey, Wade; Robinson, Davies; Payne, Webber, Broster, Birkett, Wentzel, Launchbury, Poff, Hart.
Replacements: Morris, Castex, Baker, Cannon, Vunipola, Berry, Davis, Haughton.
Referee: JP Doyle (RFU).