Caretaker boss Pearce sent out a side tough to break down in a 4-5-1 system and they looked set for a point after Claudio Reyna cancelled out Jermain Defoe's opener in the first half.
But enter Robbie Keane, the substitute on the spot six minutes from time to tap home the winner.
"A draw was probably a fair result," said Pearce. "Maybe we ran out of legs in the last 15 minutes which cost us a touch. I think we had as many decent chances as them during the game.
"There was a lot of encouraging things for me. I was pleased with the spirit we showed. I have been for the last week."
Pearce knows he needs results between now and the end of the season or his caretaker role will not be made permanent.
He added: "The result was very disappointing because I am in a results business. Being stuck on the touchline and being reasonably fit still, I was tempted to jog up that line once or twice. But you have to counter that feeling and hope that the players you send out have the same spirit.
"I was very proud of them and had we been a bit cuter in front of goal we might have snatched the game. The lads have done extremely well in my eyes but we haven't got a result. But if we keep on doing that, we will end up winning more than we lose."
Stuart Pearce felt his City side deserved some reward from his first game in charge at the Lane on Saturday.