Seconds earlier David Marshall had capped a man-of-the-match performance by keeping out Danny Webber's shot in a one-on-one situation.
Norwich kicked off attacking the River End goal and for the first quarter of the game had most of the play without troubling Paddy Kenny.
At the other end Stephen Quinn did get a shot on target, but it was too close to Marshall.
In the 13th minute the City keeper did well to save Chris Morgan's downward header from Greg Halford's notorious long throw.
After 25 minutes Billy Sharp fired wide when well placed, before Marshall made another diving save to keep out a free kick from David Cotterill.
After 37 minutes Jon Otsemobor's free-kick was comfortably held by Kenny.
Substitute Arturo Lupoli brought another save from the United keeper, then Otsemobor's goal-bound shot was blocked.
Deep in stoppage time Kenny blocked Darel Russell's shot and the ball rebounded over Lupoli's head.
Early in the second half Marshall had to save from his own player when Elliot Omozusi deflected a cross in his direction.
From that point neither side fashioned a clear cut scoring opportunity until substitute Jamie Cureton was set up by Antoine Sibierski, but his shot was an easy catch for Kenny.
Sibierski's shot gave Kenny rather more to do but he got a hand to the ball and turned it over the bar.
Eight minutes from time Russell's shot cleared the bar by inches and at the other end substitute Lee Hendrie's shot went wide by a similar margin.
Marshall came to the rescue for Norwich in the 90th minute when he pulled off a superb save to deny Webber.
Then in stoppage time Croft cut in from the right, played a one-two with Cureton before curling a left-foot shot beyond the reach of Kenny's despairing dive to his right.