Victories in their last seven league matches, including the two remaining Old Firm games at home, were needed if Celtic were to have any realistic chance of retaining their championship.
A convincing 4-1 win over Motherwell at Fir Park in the Hoops' next game was the catalyst needed and two victories over Rangers followed in the unbeaten run that ended with the title being sewn up with a 1-0 win over Dundee United at Tannadice in the last game of the season.
McManus, speaking at the launch of Celtic's new away strip for next season, praised the Parkhead fans for taking them over the finishing line.
He said: "I have no idea what happened to the fans but in the last seven games of the season they were tremendous.
"From the game against Motherwell away when we won 4-1, they seemed to give us an extra 10%.
"Every one of us came in to the dressing room after that game and couldn't believe how good our support had been.
"People don't realise how important the fans can be but that was one of the things that pushed us on."