A 15-point haul from replacement fly-half Sam Davies enabled Ospreys to come from behind to defeat Clermont Auvergne 21-13 and put them on course to reach the European Champions Cup quarter-finals.
Victory over Exeter Chiefs next weekend will see Ospreys through to the last eight after they staged a gutsy fightback at the Liberty Stadium on Friday to leapfrog last year's finalists into top spot in Pool Two.
The hosts trailed 13-6 when Davies came off the bench to deputise for Dan Biggar, who limped off with an apparent hip injury that will worry Wales coach Warren Gatland with the start of the Six Nations just three weeks away.
Davies, though, seized his opportunity by slotting over four penalties and a drop goal to change the complexion of the match.
Wesley Fofana scored the only try of the game five minutes in as Clermont made a promising start before Biggar pegged them back with a pair of penalties, the second of which came after Viktor Kolelishvili was penalised for pushing referee Wayne Barnes.
Two Morgan Parra penalties ensured the visitors had a seven-point lead at the interval, the French scrum-half's successful kicks coming either side of Kolelishvili being sin binned following an altercation with Alun Wyn Jones.
Biggar missed the target for the second time - having earlier struck the post - prior to half-time. And his night then ended early, handing Davies his chance to shine.
The 22-year-old gradually chipped away at Clermont's lead before putting Ospreys ahead for the first time with just over 12 minutes left, just after John Ulugia was binned.
Davies then made sure of the victory with two further successful penalties.