Two Clarke Carlisle headers put Watford into the Carling Cup third round.
Kenny Miller had put Wolves ahead on 10 minutes, the Scot steering a Lee Naylor free-kick past Alec Chamberlain.
But on the stroke of half-time Wolves gifted Watford the equaliser when Carlisle was allowed to head home Anthony McNamee's corner.
A cagey second-half saw the tie go into extra-time and in the 104th minute Carlisle rose to meet Matthew Spring's cross to put the Hornets through.
Watford: Chamberlain, Chambers, Carlisle, Doyley, Stewart, Spring, Bangura (Gill 102), Diagouraga (Osborne 75), McNamee, Bouazza, Francis (Grant 75).
Subs Not Used: Mariappa, Griffiths.
Goals: Carlisle 45, 104.
Wolverhampton: Postma, Naylor, Craddock, Gyepes (Lescott 45), Edwards, Davies, Cameron (Ricketts 97), Olofinjana, Seol, Miller, Ganea (Ndah 73). Subs Not Used: Oakes, Clarke.
Booked: Ndah, Lescott.
Goals: Miller 12.
After Extra Time
Ref: M Jones (Cheshire).