St Mirren boss Danny Lennon insists lightning can strike twice as his side look to shock Celtic for a second cup competition running.
Saints reached their second Scottish Communities League Cup final in four years by beating Celtic in the semi-finals last month.
In doing so, they overturned a run of eight successive defeats against the Hoops in which Saints had been outscored by an aggregate 22-0.
They now face the Glasgow giants once more on Saturday hoping to cause a second upset by knocking the Clydesdale Bank Premier League leaders out of the William Hill Scottish Cup.
And Lennon is hopeful of his team's quarter-final prospects.
He said: ``Our performances in my time here against Celtic before that semi-final were not great, not scoring a goal, never mind winning a game.
``So we know we need to be at our best.
``A lot of people have written us off already. A lot of people have asked if lightning can strike twice. My answer is why not?''
St Mirren hope to have Gary Teale fit, with the former Scotland winger having been ruled out for the past three matches with an abductor problem.
Lennon may have to do without captain Jim Goodwin who is struggling with a knock, but Kenny McLean could return following two months out with a knee injury.
Meanwhile, Celtic manager Neil Lennon played down the revenge factor.
``It's not what happened at the League Cup, it is to do with how our season will shape up between now and the end of the season,'' he said.
``We are well clear in the league after having a set-back on Wednesday night.
``I think the players are very motivated for this game and I think the fact that we lost to St Mirren in the League Cup adds a little bit more to it
``It's a quarter-final, we are away from home, we know it will be a very tough game.''
Defender Kelvin Wilson has recovered from a migraine and will be in the Celtic squad.
While Wilson returns after missing the Clydesdale Bank Premier League defeat at Motherwell on Wednesday, skipper Scott Brown is still out with an abductor problem and defender Mikael Lustig is still sidelined with a thigh injury.
Defender Charlie Mulgrew is also still out with a gluteal problem.