Wolves's Neill Collins saved face with a late winner to see off Cambridge United in the FA Cup third round.
Collins (left) and Rendell were both on target at Molineux
The Blue Square Premier side looked to be taking their Championship opponents to a replay until the defender rose to head home with three minutes remaining.
Collins had earlier handled in the box and United's Scott Rendell fired home from the spot for a half-time lead.
Wolves's recovery was sparked into life by Michael Kightly, who levelled from 12 yards before setting up the winner.
Cambridge's 4,000 travelling fans nearly saw their team go behind in the first minute when Jay Boothroyd's shot was blocked by Mark Albrighton.
But the visitors then nearly took the lead through Mark Convery, who was denied by Wolves goalkeeper Wayne Hennessey.
With the home crowd increasingly frustrated, Wolves - without a win in seven games - piled on the pressure but were repeatedly denied by United keeper Danny Potter, with Darron Gibson and Stephen Ward going close.
Wolves manager Mick McCarthy brought on Freddy Eastwood after the break and the home side began to dominate, with Ward and Eastwood missing good chances.
But it was not until shortly after the introduction of Kightly that Wolves got back into the game as the substitute fired home from Matthew Jarvis's cross.
A replay at the Abbey still looked likely until Kightly crossed for Collins to head the winner and make amends for his earlier mistake.
Wolves: Hennessey, Foley, Darren Ward, Collins, Gray, Jarvis (Edwards 90), Potter, Gibson, Stephen Ward (Kightly 60), Keogh (Eastwood 46), Bothroyd.
Subs Not Used: Ikeme, Elliott.
Booked: Eastwood, Bothroyd.
Goals: Kightly 69, Collins 88.
Cambridge Utd: Potter, Gleeson, Coulson, Albrighton, Morrison, Reed (Boylan 90), Convery (Fortune-West 90), Brown (Pitt 77), Carden, Wolleaston, Rendell.
Subs Not Used: Peters, Willmott.
Booked: Gleeson, Carden.
Goals: Rendell 42 pen.
Ref: Kevin Friend (Leicestershire).
BBC Sport Player Rater man of the match: Cambridge's Scott Rendell 8.73 (on 90 minutes).
Please note that you can still give the players marks out of 10 on BBC Sport's Player Rater after the match has finished.