Williams, who beat Henin in last year's final, won 6-2, 6-0 and will play Svetlana Kuznetsova in the semis.
After the match Williams said: "Everything worked well for me. I'm feeling better and I've keeping working hard. Being aggressive and not being 12 feet behind the baseline works."
Henin admitted that she was too defensive during the match and she did not have any courage to do anything else.
Kuznetsova made it through by beating Serna's sister Venus 6-4, 6-4.
Meanwhile in the men's tournament, Roger Federer continued his march to the final with a straight sets victory over Jose Acasuso while Rafael Nadal also made it through with a win over Paul-Henri Mathieu.
Federer faces American Andy Roddick in the quarter-finals, while Nadal will play another American, James Blake.
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