New York ? Venus Williams will head to a doctor to figure out why she felt so ill while losing to Justine Henin in the U.S. Open semifinals.

Serena Williams talked about Henin’s “lucky shots” after losing to the Belgian in the quarterfinals.

Whatever the reasons, whatever the rationalizing, know this: Henin has a chance to become the first woman to win a Grand Slam title while beating both Williams sisters along the way.

Henin reached her third U.S. Open final by beating Venus, 7-6 (2), 6-4, Friday.

“I really believed I could do it, and that’s maybe why I did,” Henin said. “I don’t think a lot of people thought I could beat her here in this tournament. I was really proud. It’s not easy to play Serena and Venus, you know.”

The No. 1-seeded Henin will face No. 4 Svetlana Kuznetsova tonight in a title match featuring two past Open champions. That will be preceded by the men’s semifinals, with No. 1 Roger Federer against No. 4 Nikolay Davydenko, and No. 3 Novak Djokovic against No. 15 David Ferrer.

Neither Williams will be there, because Venus left Flushing Meadows the same way Serena did, undone by all those big shots off the racket of the little Henin.

“I just was feeling dizzy, a little sick to the stomach. Was just having some energy problems. I’m not really sure what’s wrong with me,” Venus said. “But, you know, credit to her for playing well.”

Later, the Williams’ mother, Oracene Price, who also serves as their coach, revealed that Venus found out she had anemia after winning Wimbledon in July and had been taking medicine for the condition.