Joe Little's men looked to be heading out of the competition when striker Gary Noel struck what looked like a consolation goal in the 86th minute but two minutes later Darren Ebsworth hit home a penalty kick before Billy Jeffreys completed the great escape when he toe-poked in a scrappy equaliser in the dying seconds of the game to send the tie into extra-time.
Charlie Read headed The Lions into the lead soon after the restart then Noel scored his second of the night to set up a Third Round tie against Manchester City.
Millwall: Edwards, Sim, Ebsworth, O'Connor (Jeffreys, 50mins), Read, Bowes, Noone, Janneh, James (Rogers, 46mins), Higgins (Ofoche, 46mins), Noel. Subs not used: Chapman, Semper.