"It is special for Michael to score 100 goals in the Premiership and his four goals today were outstanding," Houllier told the club's official site.
"Michael's all round game has improved a great deal. You only succeed in this job if you have 100% effort, which he always gives.
"He has good skill, his left foot has improved, his heading is a lot better and his link up play is very good. He is a lot stronger and rarely gives the ball away.
"I think he will probably get his next 100 Premiership goals for Liverpool a lot quicker than his first."
