Managerless Tranmere earned a replay at Leyton Orient as Chris Shuker cancelled out Luke Ashworth's early header.
Ashworth nodded Orient ahead from Sean Thornton's inviting corner, and Glenn Morris kept the visitors ahead with two fine diving saves to thwart Shuker.
But after the break Tranmere were again the more creative and were rewarded for their possession as Shuker found the net with a sweetly-struck effort.
Morris turned over a close-range effort by Craig Curran as Orient held on.
Tranmere caretaker manager Les Parry told BBC Radio Merseyside:
"We've got to look at ourselves, being disappointed at half-time coming in 1-0 down. Apart from that, we have dominated the first half.
"Second half, I think the lads applied themselves brilliantly, we sneaked a goal and there were other chances when we could have taken the lead."
Leyton Orient manager Geraint Williams told BBC London 94.9:
"That's probably as disappointed as I've been in the performance since I've been at the club.
"I'm very relieved that we have got a replay. We had nothing going forward.
"Defensively, we weren't the best either. Thanks to our keeper we're in the hat for the next round with a chance to get through."
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