Ospreys coach Steve Tandy described the comeback win over Clermont Auvergne as one of their finest results in Europe.
Sam Davies came off the bench to kick 15 unanswered points as the Welsh side recovered from seven points down to win 21-13 in the Champions Cup on Friday.
The win puts Ospreys two points clear of Clermont at the top of Pool Two with an away game against Exeter to follow.
"It was an amazing effort. There haven't been too many days when I've been prouder of this team," said Tandy.
"When you put it in context of how youthful the squad is and when you look at the finances of the French and English teams it's got to be up there with one of our best.
"But ultimately, we still haven't achieved what we want to do. Before we played Exeter in the first game, the one thing we had was belief in ourselves.
"We've still got one more game to go otherwise it will be all for nothing."
Victory and a quarter-final place seemed to be slipping away as Clermont dominated the first half in Swansea.
The Ospreys pack was completely outplayed, and the backs seemed desperately short of inspiration and imagination.
The cause looked lost when fly-half Dan Biggar hobbled off early in the first half with a dead leg, but replacement Davies proved to be the match winner as he took full advantage of the French side's indiscipline.
"Nothing flusters him, doesn't matter who he's up against," said Tandy of the 22-year-old, whose 79th-minute penalty also denied Clermont a losing bonus point.
"It's not going to worry him. He truly believes he can do it on any stage, which is a real positive.
"But it's making sure we get that consistent performance from Sam week-in-week-out."
Ospreys will now head to Exeter on 24 January with their destiny in their own hands, hoping to reach the last of Europe's premier cup competition for the first time in six years.
And Tandy added: "It's no good us getting carried away even though it's an amazing win and probably one of our finest but ultimately it will count for nothing if we don't go an finish off the job in Exeter, which will be tough.
"It's a job half done."