Inspired by the return of their World Cup stars and a titanic cameo from James Haskell, London Wasps hauled themselves back from a 26-8 deficit to record a fine 29-26 victory over Gloucester in Sunday's EDF Energy Cup clash at Adams Park.
Wasps, with only one victory from their previous seven matches this season as World Cup calls decimated their playing resources, looked down and out after Gloucester scored their fourth try through wing Iain Balshaw in the 65th minute of the game.
But the introduction of a wave of replacements, including French World Cup skipper Raphaël Ibanez and Haskell, and the switch of talented teenager Danny Cipriani from full-back to fly-half, transformed the Heineken Cup holders.
Haskell, the most controversial absentee when England coach Brian Ashton made the final cuts to his World Cup squad, went over in the 66th and 73rd minutes for tries - both converted by Cipriani - as the Wasps pack turned the tables after being outplayed for the first hour.
A desperate tackle by Gloucester forward replacement Gareth Delve, who dived full-length to tap the ankle of England winger Paul Sackey, playing his first match since returning from the World Cup, looked to have denied Wasps their unlikely victory.
But with 20 seconds of normal time remaining, the Wasps forward drove over the Gloucester line again for the winning try, credited to second-half substitute John Hart.
Hart was the 61st-minute replacement for skipper Lawrence Dallaglio who was withdrawn before Wasps launched their fightback.
Dallaglio, embroiled in controversy for his scathing attack on England coach Ashton since arriving back from the World Cup, was signing copies of his autobiography in the club shop after the match.
But he had failed to make his mark on the Wasps pack which came of decidedly second best for much of the game.
Gloucester, who took the lead when scrum-half Rory Lawson wrong-footed the home defence with a delightful dummy which took him past Wasps fly-half Riki Flutey, struck again in the 34th minute.
A spell of forward pressure resulted in hooker Olivier Azam forcing his way over for their second try, with fly-half Ryan Lamb again converting to put them 14-0 ahead.
World Cup referee Wayne Barnes, who failed to spot a French forward pass as New Zealand were knocked out of the World cup, did not endear himself to the Wasps supporters.
He disallowed a 10th-minute Sackey try because of an earlier infringement and then denied Tom Voyce by awarding a penalty instead of allowing the advantage.
Cipriani kicked the penalty in first-half injury time but Wasps looked dead and buried early in the second half.
The Gloucester number eight Luke Narraway was stopped inches short of the tryline after bursting through the middle, once again exposing the frailties of the normally so-solid Wasps defence.
But the ball was moved quickly out wide with Lamb and James Simpson-Daniel combining to send full-back Olly Morgan over in the right-hand corner for a try which Lamb converted.
Voyce rushed a tackle from Simpson-Daniel to score Wasps' opening try in the 53rd minute but Gloucester struck again when Anthony Allen and Morgan set up Balshaw's 61st-minute try to stretch their lead to 26-8.
The yellow card which dispatched Gloucester second-row man Peter Buxton to the sin-bin for the final 10 minutes proved decisive as Wasps utilised their extra-man advantage to the full to complete a remarkable turnaround.
Their bonus-point victory puts them level at the top of Pool A with Newcastle Falcons, with the group decider to be played at Wasps' Adams Park Ground on the last weekend in November.
For London Wasps:
Tries: Voyce, Hart, Haskell 2
Cons: Cipriani 3
Tries: Morgan, Azam, Lawson, Balshaw
Cons: Lamb 3
London Wasps: 15 Danny Cipriani, 14 Paul Sackey, 13 Fraser Waters, 12 Rob Hoadley, 11 Tom Voyce, 10 Riki Flutey, 9 Eoin Reddan, 8 Lawrence Dallaglio, 7 Tom Rees, 6 Dan Leo, 5 Richard Birkett, 4 George Skivington, 3 Nick Adams, 2 Joe Ward, 1 Tim Payne.
Replacements: 16 Raphaël Ibañez, 17 Michael Holford, 18 John Hart, 19 James Haskell, 20 Simon Amor, 21 Dave Walder, 22 Mark Van Gisbergen.
Gloucester: 15 Olly Morgan, 14 Iain Balshaw, 13 James Simpson-Daniel, 12 Mike Tindall, 11 Mark Foster, 10 Ryan Lamb, 9 Gareth Cooper, 8 Luke Narraway, 7 Akapusi Qera, 6 Alasdair Strokosch, 5 Alex Brown, 4 Peter Buxton, 3 Carlos Nieto, 2 Olivier Azam, 1 Nick Wood.
Replacements: 16 Andy Titterrell, 17 Patrice Collazo, 18 Will James, 19 Gareth Delve, 20 Rory Lawson, 21 Chris Paterson, 22 Anthony Allen.
Referee: Wayne Barnes (England)
Touch judges: Andrew Watson (England), Ken Stewart (England)
Television match official: Bob Ockenden (England)