Helder pounced on Trevor Sinclair's miscontrol in the area to curl home our second goal in the 3-1 fourth round victory.
Darren Anderton had earlier put us 1-0 up, City came back into it after the break and replied with 10 minutes left only for substitute Fredi Kanoute, back after six weeks out, to seal the win in injury time.
But the talk was of Helder's first goal afterwards. "I am delighted for Helder," said acting boss David. "He is only 20, he is in another country and he has scored a goal. He'll grow from that."
There was real energy to our play as we forged ahead in that fine first half display - David conceded afterwards that it was no surprise that City came storming back in the second half.
"When you go 2-0 up in a cup tie you expect the kitchen sink to come at you because they have got nothing to lose," he added.
"We are not quite good enough to maintain the ascendancy for longer enough periods.
"We looked dangerous on the break, which was good, but our hearts were in our mouths and the defending and the blocking was fantastic.
"Kasey held his hands up with a mis-cue for the goal, but I have to say that Doherty, Gardner and King are all 23 and that threesome in the centre, against some very bright players, did us proud."
David Pleat paid tribute to Helder Postiga after the Portuguese striker bagged his first goal for the club in last night's Carling Cup win against Manchester City.