Heskey came off the bench just before the hour mark to score the equaliser and then helped Ashley Young to grab a brace.
Houllier said after the game: "I know what Emile can do. He showed a few things in training to indicate he was in good form.
"He was decisive. With Emile it's a matter of confidence. It's the same with all strikers, but probably more so with him.
"Emile came on and was showing freshness, scored one goal and played a part in the other two.
"I was not disappointed by the effort and application in the first half but there was no flow to our game, but I changed the system in the second half and I thought it suited the players more.
"I did not feel down at half-time. I have seen the team a bit in training and I thought it was a matter of getting ourselves into the game."