They were made to pay when Preston North End substitute Neil Mellor, whose father used to play for the Canaries, scored an excellent goal to earn his side a point.
Norwich kicked off attacking the River End goal, but when David Marshall failed to deal with Paul McKenna's cross from the right, Barry Nicholson's shot was cleared off the line and former Canary, Chris Brown, followed up to smash the ball high into the net from seven yards.
Things got worse for Norwich when Dejan Stefanovic had to be stretchered off with his left leg in a brace.
Gary Doherty replaced him at the centre of the City defence.
In the 14th minute, David Bell put in a left-wing corner and Leroy Lita equalised when he out-jumped the Preston defence to plant a firm header into the net.
After 28 minutes, Andrew Lonergan pulled off an acrobatic save to block a fierce shot from Lita.
Three minutes later, Ryan Bertrand's shot came back off the bar and Lee Croft put his shot wide.
In first-half stoppage time, Antoine Sibierski limped off and was replaced by Jamie Cureton.
Thirteen minutes into the second half, Bell's shot was saved by Lonergan.
However, the Preston keeper was beaten a minute later from close range at the far post when John Kennedy got his right foot to Bell's free-kick from the left wing.
Jon Otsemobor elected to pass when he could have had a shot and Cureton followed suit.
Darel Russell was shown a red card for handing off a Preston player after the referee had awarded him a free-kick.
Within two minutes, two of the Preston substitutes combined for the equaliser.
Richard Chaplow passed to Mellor and his crisp, right-foot shot from 20 yards beat Marshall's despairing dive to his right.