Harlequins kicked off their Aviva Premiership title defence with a thrilling 42-40 victory over Wasps in the London Double Header at Twickenham on Saturday.
Conor O'Shea's men seemed dead and buried as the rejuvenated Wasps, who had only avoided relegation on the final day of last season, stormed into a 40-13 lead after 56 minutes.
Christian Wade did the early damage, scoring two blistering tries and providing another for Tom Varndell before forwards Marco Wentzel and Tim Payne touched down.
Man of the Match Nick Evans, on his 100th Premiership appearance, scored 22 points to lead Harlequins on one of the great Premiership comebacks, though.
The reigning champions, back at the scene of their Premiership final victory over Leicester, scored four tries and 29 unanswered points in the final quarter of a compelling match.
Tom Guest came off the bench to launch the comeback, Evans set up two tries for Mike Brown and then touched down himself before wrapping up the victory with a penalty four minutes from time.
For all the drama on show, there was also a hefty dose of controversy as the introduction of new rules expanding the influence of the Television Match Official (TMO) proved crucial.
Wasps thought they had scored through Varndell on the stroke of half-time but the try was chalked off after the TMO confirmed a forward pass early in the move. Had this game been last season - or not broadcast live on ESPN - Varndell's try would have stood.
Wasps players lay desolate on the turf at full-time. They had two bonus points but knew that, through some weak defence, they had blown a golden opportunity. The performance of Dai Young's men for the first hour did at least indicate the horrors of last season do now lie behind them.
Harlequins like to play at pace but they could not live with Wasps. The dark days of March, April and May when the club were desperate to just grind out any kind of result to secure survival seemed long gone.
It took just three minutes for Wasps to fashion the first opening as Varndell released the electric Wade to round Brown and score. Robinson converted two penalties to extend the lead before the wing twins of Wade and Varndell combined again.
Hugo Southwell ran onto Elliot Daly's flat pass and released Wade, who again scorched past Brown and over the try-line, only to inexplicably pass to Varndell instead of touching down.
If Wade's decision caused brief palpitations in the Wasps coaching box, the mood will have been eased by Varndell touching down and Robinson converted to open that 20-0 lead. The champions, who had barely had the ball, responded with a quick tap from Danny Care and Tom Williams collected Robshaw's offload to score under the posts.
Wasps were relentless. After a third Robinson penalty, Jonathan Poff forced a turnover and Wade produced an exceptional finish to score his second try. In a moment reminiscent of Jason Robinson's try for the British & Irish Lions in the first Test against Australia in 2001, Wade stood up his opposite number George Lowe and then scorched past him on the outside.
Evans reduced the arrears with two more penalties before Varndell streaked away on the stroke of half-time for what looked like Wasps' bonus-point try. The celebrations were cut short after referee Greg Garner utilised the trial rules and asked TMO Graham Hughes to rule on a suspected forward pass from Robinson early in the move.
The try was duly disallowed and for a while it seemed academic. Seven minutes into the second half, Varndell pounced on a mistake from Mo Fa'asavalu and then flicked the ball in-field for Wentzel to gallop over from the 22m line.
Wentzel then turned provider, exchanging deft passes with Payne for the loose-head prop to crash over the line from close-range at the end of another dynamic attack. Wasps led 40-13.
With the game seemingly gone, Harlequins exploited some weak Wasps tackling to stage their late rally. Initially it seemed a try bonus and maybe a face-saving losing bonus point was the best they could hope for.
Guest came off the bench to score with his first touch before Brown showed some excellent hands to take a quick pass from Evans and dive over in the corner.
When Evans picked out Brown with a raking cross-field kick, the England fullback scored Harlequins' fourth try - but they were not finished yet. Brown squeezed an offload to Guest and Evans took advantage of more poor defence to wriggle through two tackles and touch down for Harlequins' fifth try. The conversion took Harlequins to within a point and Evans rounded off a remarkable comeback with his penalty four minutes from time.
And after the match, Quins boss Conor O'Shea admitted that it was something he never wanted to experience again. "I did think the game was gone. Our set-piece was poor, our discipline, they won the contact areas and when we turned the ball over they stung us," O'Shea said. "It was a long way back - but we got a lot of energy from the bench.
"That try Guest scored from the charge-down just gave us a little bit of hope. The more we played, the more we held onto the ball. We started winning the collisions, we got our offloading game going. We are delighted to get away with that but we know defensively we are miles better than that.
"We didn't bring our game. Thankfully we have got away with it. It is the rocket we need, potentially."
His opposite number, Dai Young, was pleased with his team's efforts saying: "For 50 minutes we probably played as well as we have done since I have been at the club. We talked at half-time about not switching off and keeping our concentration and how good a team Quins were and that they would keep playing.
"Things that weren't sticking for them first half and were sticking for us, it was always going to change. It wasn't a surprise for us. I thought the charge-down kick gave them that momentum and for the last 30 minutes we struggled to get our hands on the ball."