James Hook banged over a dramatic conversion with the last kick of the game to complete a stunning win against English champions Sale Sharks.
The Heineken Cup started with a bang as Shane Williams skipped over for his second try of the game seven minutes into injury-time and Wales centre Hook kept his cool to clinch a remarkable win.
The Ospreys triumph was all the more remarkable having trailed Sale since the 50th minute following three Charlie Hodgson penalties and Juan Fernandez Lobbe's try.
But following a non-stop barrage of attack by the Welsh region - wing wonder Williams darted over off Lee Byrne's pass and Hook, a second half replacement, sparked delirious scenes at the Liberty Stadium with his conversion.
Ironically the 21-year-old would not have had the chance had regular penalty taker Gavin Henson not failed a late fitness test on a strained
Replacement Shaun Connor gave the Ospreys an ideal start with a penalty inside two minutes. That start got all the better when Williams burst over in the corner for the opening try on seven minutes.
Justin Marshall broke free after the Ospreys forwards stole possession, Connor was twice involved in the swift counter-attack, the second time passing to Williams who dived through Oriol Ripol's goal-line tackle to score.
Connor converted but a Byrne blunder saw Sale hit back straight from the kick-off. The Wales full-back saw his clearance blocked by Hodgson and No8 Lobbe had the simplest of touch downs.
Sale lost England star Mark Cueto to an ankle injury and then saw nine points go begging in the space of five minutes before half-time.
Outside-half Hodgson missed two shots at goal before Cueto's replacement, Daniel Larrechea, also missed from long range.
The Ospreys also missed their chances, Connor hitting the post with a penalty before sending clear Nikki Walker who failed to spot Sonny
Parker unmarked by his side.
And they ended the half down to 14 men when Brent Cockbain was shown the yellow card for foul play.
Hodgson rediscovered his range, levelling the scores 10-10 on the stroke of half-time before giving Sale the lead for the first time in the game with a 50th minute strike.
With the scores s close, both side's turned to their bench in a bid to swing the game, Sale bringing on the imposing figure of Sebastien Chabal while the Ospreys turned to young James Hook who snatched at a speculative drop goal with his first touch.
That was what the Ospreys were left with as they were starved by possession by the Sharks pack in a tightly contested second half.
Hodgson knocked over a third penalty four minutes from time that looked to have won the game until Williams and Hook struck late on.
Ospreys: Tries - S Williams (2). Cons - S Connor, J Hook. Pens - S
Sale Sharks: Try - JF Lobbe. Con - C Hodgson. Pens - C Hodgson. (3)
Referee: Joel Jutge (France)