City led 1-0 after dominating the first half but the tables were turned in the key opening 20 minutes of the second half.
The arrival of substitutes Stephane Dalmat and John Jackson for injured pair Darren Anderton and Mauricio Taricco gave the side fresh imputus and chances were created before and after Gary Doherty's equaliser on 56 minutes.
City rallied late on but after a few nervous moments, the fourth round tie ended 1-1.
"I was filled with pleasure at the way we were able to come back from such a mediocre first half - and that's being kind - to play so well and change the game so dramatically," said David afterwards.
"We played with such a young side and it was such a vibrant performance in the second period, full of character.
"I'm pleased for the supporters. I'm sure they wouldn't have known what to do at half-time but they can go back now with hope for the second game."
We could have scored another couple of goals but having said that, when City came again at the death, they could have had a couple of goals too.
He's filled in excellently for Richards. He's a centre-half who when he goes up for set-pieces is always likely to get a goal. If you look at his Luton record it's a fantastic record but three-quarters of his games were at centre-half. He used to go up and score goals. He had a knack. I had another player like that in Steve Foster at Luton, the ball seems magnetised to their heads. It was a great corner from Postiga and that was something we worked on, so I was pleased with that.
David Pleat has expressed his satisfaction with the growing understanding between strikers Robbie Keane and Helder Postiga.
Helder has stepped in for Fredi Kanoute - on African Nations Cup duty with Mali - in the games against Liverpool and Sunday's FA Cup tie at Manchester City, scoring against the Reds a fortnight ago.
"I was delighted with the way Postiga dovetailed with Keane," said acting boss David after the 1-1 draw at the City of Manchester Stadium.
"In the second period they played well together and it was a combination worth seeing.
"The fact that Dalmat is in a wide position attracts that little more attention so there is more space to play into the front players.
"I thought they were very good. They worked very hard and looked a partnership, looked as if they could play together."
David Pleat revealed that Mauricio Taricco and Darren Anderton were withdrawn because of injury at City yesterday.
Defender 'Tano' took a couple of knocks in the first half and needed stitches after suffering a head injury.
Acting boss David said midfielder Darren was suffering from tendonitis.
Both players played until half-time but were replaced by John Jackson and Darren Anderton at the interval.
A stirring performance in the second half secured a draw and a replay at the Lane on Wednesday February 4.
"Taricco is very sore," reported David last night. "The doctor did a fantastic job at half-time, there was lots of blood and it was like emergency ward 10.
"He got him stitched but his foot beat him. The head injury didn't beat him, it was his foot.
"Darren was a bit sore before the game, a bit of tendonitis and he was honest enough at half-time to say 'I'm struggling' but there was no question I was going to change things around anyway.
"Stephane Dalmat came off at half-time last week against Liverpool with a bit of a back problem. He had an injection at the start of the week.
"I decided to go with that team and to make the changes at half-time because we were carrying a couple of injuries."
REPLAY TICKET DETAILS...
David Pleat was 'filled with pleasure' by our second half comeback in the FA Cup at City - and reserved special praise for our travelling support..