A 92nd minute converted try to Ospreys Rugby handed Leicester Tigers their first defeat of the 20222/3 Heineken Champions pool stages on Friday evening.
After holding out Ospreys for 12 minutes following the conclusion of regular time, a try to Jac Morgan from the base of the ruck - and conversion from Owen Williams - sealed the result for the Welsh visitors in front of almost 20,000 fans at Mattioli Woods Welford Road.
Nothing separated the sides at half-time, level at 13-all, before two second-half scores from Ospreys helped secure the away win.
The home side were the first to register points, just four minutes into the match, when Handré Pollard kicked the first of what would be six successful attempt from the Leicester fly-half.
Ospreys got on the scoreboard in the 11th minute with a try to Dewi Lake at the back of a driving maul from close range and full-back Cai Evans converted to see them lead by four points, 3-7.
The Tigers scrum-half popped a well weighted pass up for Harry Simmons, who appeared to have scored Leicester’s second in the 19th minute, after the left wing swerved his way through the Ospreys defence to dive over under the posts.
However, TMO intervention scrubbed the score from the board after it was deemed to have been held up.
Play was brought back to near halfway and Pollard added three points to extend the lead to 13-7 on the 20 minute mark.
Just five minutes later, Ospreys responded with a penalty-goal of their own to Williams to make the difference three points.
Forced to defend for much of the final 10 minutes of the first-half, Tigers continued to send Ospreys away before the pressure mounted and infringements piled up from the home side.
With seconds remaining before the break, Williams stepped up to level the scores at 13 a piece at half-time.
After being denied in the first-half, there was no question marks when Simmons dived over in the 49th minute after injecting himself into a backline move to the right hand side in attack.
On the back of a monstrous effort from the pack, the left wing ran through untouched from 10m out and Pollard converted to see Tigers out to a 20-13 lead.
Piling pressure on in attack, Tigers looked likely for another before the ball went to ground out wide and Ospreys pounced.
The loose ball was toed ahead and bounced up into the hands of Keelan Giles, who raced away to score under the posts.
Williams converted and, again, the sides were level.
Pollard kick two successive penalty-goals in the 67th and 70th minutes to put Tigers ahead, 26-20, before the home side were forced to defend for almost the remainder of the game.
The TMO was called upon on back-to-back occasions as Tigers continued to fight for every inch.
Dan Richardson was shown a yellow card in the dying stages, bringing James Whitcombe back onto the field, and Ospreys persistence paid off when Morgan was ruled to have scored in the 92nd minute after a long-waited deliberation from the officials on the field and in the video box.
Williams conversion from near in front sealed the win for Ospreys, 26-27.