London Wasps clinched a famous victory over English champions Harlequins at The Stoop thanks to a 17-16 scoreline.
The win propelled Wasps back into the playoff positions above Gloucester, with Harlequins missing out on retaining top spot after Leicester picked up a win earlier on Saturday.
Wasps started with a bang thanks to an interception try from Tom Varndell, the winger pouncing on a loose pass from Nick Evans to Ugo Monye to hand advantage to the visitors.
Evans was unable to atone for his error as an early penalty shot drifted wide, but it was Wasps who struck next through a thrilling counter-attack.
The initial break from Elliot Daly down the right freed up space for Chris Bell, who found the blazing Christian Wade on his outside for Wasps second try of the match and a 14-0 lead.
Evans found his range to put the hosts on the board, before centre Matt Hopper was found out on the left wing and ran in untouched to leave the score at 10-14.
Harlequins added another three more points right at the end of the first half from Evans' boot to narrow the gap to just a point going into the interval.
A frenetic opening to the second half generated plenty of running rugby and chances for both sides at either end, Christian Wade coming close down the right touchline before being thumped into touch by Monye.
Robinson added three more points to stretch the lead to four again and Evans failed to hit a penalty opportunity of his own with 12 minutes remaining.
A break around the fringes from Harlequins scrum-half Karl Dickson created another opportunity for points from the resulting scrum, with Evans this time obliging to leave the gap at just a single point.
Centre Elliot Daly shanked a long-range kicking opportunity with six minutes remaining, failing to increase Wasps' narrow lead as time ticked away.
Harlequins then turned over possession and began a series of punishing drives into the Wasps half, winning a crucial penalty for offside from 40 metres out which Evans elected to go for.
His attempt was typical of his afternoon in falling wide to the right, leaving Harlequins with only a minute remaining on the clock to find the crucial points.
It wasn't enough time, as Wasps clinched a first victory at The Stoop over their London rivals since 2007 - a result that would have been unthinkable this time last year when they were in the midst of a relegation battle.
Pens: Evans 3
For London Wasps:
Tries: Varndell, Wade
Cons: Robinson 2
Harlequins: 15 Ross Chisholm, 14 Tom Williams, 13 George Lowe, 12 Matt Hopper, 11 Ugo Monye, 10 Nick Evans, 9 Karl Dickson, 8 Nick Easter (c), 7 Luke Wallace, 6 Tom Guest, 5 George Robson, 4 Charlie Matthews, 3 James Johnston, 2 Joe Gray, 1 Mark Lambert.
Replacements: 16 Rob Buchanan, 17 Darryl Marfo, 18 Will Collier, 19 Sam Twomey, 20 Maurie Fa'asavalu, 21 Ollie Lindsay-Hague, 22 Rory Clegg, 23 Jordan Turner-Hall.
Wasps: 15 Hugo Southwell (c), 14 Christian Wade, 13 Elliot Daly, 12 Chris Bell, 11 Tom Varndell, 10 Nick Robinson, 9 Joe Simpson, 8 Billy Vunipola, 7 Sam Jones, 6 Ashley Johnson, 5 Marco Wentzel, 4 James Cannon, 3 Phil Swainston, 2 T Rhys Thomas, 1 Zak Taulafo.
Replacements: 16 Tom Lindsay, 17 Tim Payne, 18 Will Taylor, 19 Alex Rae, 20 Tinus Du Plessis, 21 Charlie Davies, 22 Stephen Jones, 23 Charlie Hayter.