McCann tucked away a 79th-minute spot-kick to earn Posh a 1-1 draw against promotion-chasing Hull at London Road. It was a first positive result from a losing position all season for the strugglers.
The Northern Ireland international made no mistake after skipper Tommy Rowe had been upended by James Chester - a one-time Posh loanee.
Veteran McCann celebrated his strike by diving into a big pile of snow. The match only went ahead after an army of around 60 supporters cleared the pitch.
In the process he spared the blushes of young team-mate Joe Newell who had swiped a Robert Koren corner into his own net to hand the visitors the lead.
Posh boss Ferguson said: "A point was the least we deserved and I wouldn't have been surprised if we had gone on to win after getting ourselves level.
"It was harsh on us to fall behind to a mistake from young Joe, but he is a lad with an excellent temperament and didn't let if affect him.
"The most pleasing thing was seeing our substitutes come on and change the game. Grant in particular upped our tempo, got hold of the ball and tucked away the penalty.
"Home form is crucial when you are fighting to stay up and I know for a fact that the relegation battle is going to go right down to the wire.
"There is no doubt in my mind we have enough quality to stay up but it was doubly-important for us to play as we don't have a game next weekend. I must thank all the people that helped to get it on."
- Sports & Recreation