Morten Gamst Pedersen scored twice but Houllier felt the defeat owed more to his players' inability to make the most of their opportunities to score.
"I don't think we gave a fair account of ourselves," Houllier said.
"We had a couple of chances in the first half and when you are away from home, you need to take those chances - otherwise you can be punished.
"We then conceded a goal probably at the worst moment in the game, in (first-half) added time.
"It puts you in a different position because you know they are then going to play deeper and more defensive, and deny us space."