Cardiff Blues went into the game in Coventry with an unbeaten record in the competition – after victories over Newcastle and Scarlets – and with the chance to move to the top of the pool standings as they chased a semi-final spot.
However, they looked doomed after a breathless opening half that saw seven tries and 52 points as both teams played an attacking brand of rugby in the Midlands.
Blues were 42-17 down with less than half an hour to go before four unanswered tries saw them roar back and claim the most incredible win to spark wild celebrations.
Leicester Tigers now arrive at BT Sport Cardiff Arms Park next Saturday afternoon and another victory would ensure a place in the final four of the cup.
Wasps – undefeated at their new home – had blasted into a commanding lead with three tries in the opening quarter and had the bonus point wrapped up by half-time, with former Blues player Thomas Young grabbing two.
Spirited Blues showed plenty of battling qualities in adversity with two quick-fire tries at the midpoint of the half, from Macauley Cook and Lewis Jones, but had it all to do by the break as the home pack took control.
Guy Thompson scored four minutes after the break before three tries in eight stunning minutes from Miles Normandale, Lucas Amorosino and Seb Davies put Blues just four points behind. And then Nomandale blasted over with time up.
The game had started quietly with Wasps looking to use their power up front and full back Alex Lozowski missing an early penalty attempt.
Lozowski made amends soon after and was a big part of the opening try as he made yards before lock James Cannon bulldozed through men. Slick hands down the right then sent wing Will Helu over with Lozowski nailing the conversion to start a hugely impressive 15-minute spell from the hosts.
Young was held up over the line after relentless home pressure before a grubber in behind almost sent Josh Bassett over.
It was the home forwards, though, that were really fronting up and they secured second home score as a penalty try was awarded by referee Tom Foley after big home scrum to make it 14-0 after as many minutes in Coventry.
Rhys Patchell missed with a penalty attempt before he was called upon to haul Will Rowlands into touch as the last man as Wasps again split open the Blues defence.
There was no stopping a third home try as power up front against proved decisive as Young bashed over for 21-0 lead.
Blues had been living on territorial scraps, but when they finally worked a position they were clinical as Cook crashed over after neat handling in the build-up by the forwards.
Patchell added the extras and five minutes later the lead was cut to seven as a quick tap penalty sent Lewis Jones close. James Sheekey picked up at back of the resulting scrum and rattled up to the line before livewire Jones spotted a gap and dived over.
However, comeback hopes appeared to be snuffed out within three minutes as more direct running from the home back line opened up space and Sailosi Tagicakibau slid in the corner after handing off two tacklers.
Patchell cut the lead with a penalty, but the final word of the exhilarating opening 40 minutes went to Wasps as anther lineout drive saw Young touch down for a 35-17 lead.
Joaquin Tuculet tried to put Blues back on the front foot at the start of the second half with a jinking run from deep, but it was the home side that struck within four minutes as home Number Eight Guy Thompson brushed off a tackle and raced over.
And then the tide started to turn as Blues took control and produced a 30-minutes of rugby few fans in the crowd of 9,630 will forget.
First the game’s theme of forwards making the biggest impact continued as Normandale picked up and dived over the line from close range for a third away try, after Ellis Jenkins went close after a slicing run.
Belcher and Tuculet then almost combined to send the dynamic young hooker over, before Argentine wing Amorosino took Patchell’s neat reverse pass in his stride to dance his way over for a bonus point.
Moments later lock Seb Davies broke tackles, after more wonderful handling from the inspired visitors, and the lead was down to 42-38 with the final quarter to come.
A fast and frenetic last ten minutes saw both teams have chances before, with 17 seconds left, Patchell kicked to the corner from a penalty.
The forwards kept the ball alive time and time again as they probed for an opening after numerous phases. Then a break from Amorosino, Normandale picked up and as his team-mates surrounded him he was driver over.
Patchell added the extras from out wide and the referee signaled the end to almost disbelief from the home crowd. Blues were top of the pool and, with one game to go, semi-final hopes are very much alive.
Timeline:
08m Helu t Lozowski c7-0
14m Penalty t Lozowski c 14-0
22m Young t Lozowski c 21-0
27m Cook t Patchell c 21-7
32m Jones t Patchell c 21-14
35m Tagicakibau t Lozowski c 28-14
38m Patchell p 28-17
40m Young t Lozowski c 35-17
44m Thompson t Lozowski c 42-17
53m Normandale t Patchell c 42-24
57m Amorisino t Patchell c 42-31
61m Davies t Patchell c 42-38
80m Normandale t Patchell c 42-45
Cardiff Blues: 15 Joaquin Tuculet, 14 Richard Smith (Walsh 66), 13Garyn Smith (Humberstone 71), 12 Adam Thomas, 11 Lucas Amorosino, 10 Rhys Patchell, 9 Lewis Jones (T Williams 54); 1Thomas Davies (Thyer 71), 2 Rhys Williams (Belcher 50), 3 Craig Mitchell (D Lewis 56), 4 Miles Normandale, 5 Seb Davies (Roach 63), 6 Macauley Cook, 7 Ellis Jenkins, 8 James Sheekey
Replacements: 16 Liam Belcher, 17 Brad Thyer, 18 Dillon Lewis, 19 Ben Roach, 20 Jordan Viggers, 21 Tomos Williams, 22 Simon Humberstone, 23 Geraint Walsh