Goalkeeper Artur Boruc revealed how memory served him well as he saved Louis Saha's late penalty to book Celtic a place in the Champions League knock-out stages for the first time.
Manchester United striker Saha was denied from the spot by Boruc with barely a minute of regulation time still to play.
The Parkhead side had been second best for most of the match but took a sensational lead nine minutes from the end when midfielder Shunsuke Nakamura's stunning free-kick from 25 yards sailed past Edwin van der Sar.
As Celtic Park rocked, there were two more moments of drama to come, a missed sitter by United striker Saha and the Frenchman's penalty.
Poland international Boruc took heed of the way Saha shot when he scored from the spot in United's 3-2 win over Celtic at Old Trafford in September - and went the correct way, diving to his right to palm away a firm strike.
Boruc said: 'I don't know about it being a great save from the penalty. Every time a `keeper saves a penalty it's luck, that's all.
'I was thinking about the last penalty he scored against me and I thought he might do the same thing, that's what was on my mind.
'We were celebrating in the dressing room when someone came in the with news that we had qualified and so there was a double celebration.'
Boruc was equally diffident about his save from Saha just minutes before the penalty.
The United striker appeared to believe he was offside when he was played in by Wayne Rooney.
Saha hesitated, as did most players in the anticipation of a flag being raised, and Boruc rushed from his goal to block the Frenchman's feeble effort.
Boruc said: 'I didn't see that he was offside, I just played on.'