Nick Evans put in a man-of-the-match performance upon his final Harlequins appearance at The Stoop as Premiership leaders Wasps were beaten 32-13.
The former New Zealand international joined Quins back in 2008 and produced a timely reminder of his enduring quality as the home side kept their faint hopes of a play-off place alive.
Quins sit six points adrift of fourth-placed Leicester Tigers, with a top-six finish and automatic qualification for next season's European Champions Cup a more realistic possibility.
As for Wasps, defeat leaves them five points clear of Exeter Chiefs and facing a possible showdown for a home semi-final when Saracens visit the Ricoh Arena on the final day of the campaign.
It was Evans' penalty that broke the deadlock, but it was Wasps who led 10-6 at the break after Jimmy Gopperth took a high ball and freed Dan Robson to score.
The second period was all Quins, though, Chris Robshaw evading Kurtley Beale's interception attempt and feeding Tim Visser to go over in the left corner.
Evans added the extras and four more penalties – two of which came after yellow cards to Willie le Roux and Joe Launchbury – to underline Quins' dominance, before Joe Marchant's late try enabled Evans to slot over two more points before he left the field to a standing ovation in the final minute.
In Friday's other game, Sonatane Takulua scored all of Newcastle Falcons' points in their 16-14 win over Worcester Warriors.