United won the game 2-0, with Diego Forlan embarrassing Jerzy Dudek with two gifted goals.
But Houllier insists the Reds have a score to settle and believes a victory could transform Liverpool's season.
"We have something to wipe out of our heads after what happened last year," he said.
"You never know what will happen in a season. Last year United were eight points behind Arsenal and still went on to win it."
