NEW YORK -- Serena Williams won't face her big sister in the U.S. Open semifinals, but she will take on a close friend in a battle of former Open champions.
The defending champ and No. 2 seed, Serena advanced to face unseeded wildcard Kim Clijsters in Friday's semis by virtue of an impressive 6-4, 6-3 victory over No. 10 Flavia Pennetta in Arthur Ashe Stadium.
Clijsters, the 2005 champ who is playing in just her third tournament since coming out of retirement, advanced earlier with a straight sets victory over No. 18 Li Na of China. The Belgian mom previously downed Venus Williams in a three-set epic in the fourth round.
"[Clijsters] is such a great person. I only wish the best for her, obviously, but not in my next match," Serena said in her on-court interview.
"Regardless, it will be a great match. She has nothing to lose and she's just having so much fun. Seeing how much she enjoys the game, it makes me so happy."
Serena smacked a forehand passing shot down the line on her second match point against Pennetta and then pumped both fists as she bellowed out a scream that echoed throughout Ashe.
That shot signified her dominance of the match and the tournament. Serena has not dropped a set through five matches and has lost only 24 total games. Against Penneta, she banged out seven aces while making just one double fault and produced 22 winners against 19 unforced errors.
"She was playing really well. She was very aggressive," said Pennetta, the first Italian women ever to crack the top 10.
"For me, Serena and Venus are the best one," Pennetta added. "When they are in shape and when they are fit, they are the No. 1."
Regardless of whether or not she wins the Open, Serena will remain No. 2 in the world behind Dinara Safina, who was bounced in the third round and has yet to win a major.
But Serena continues to prove she is the best player in the world when it counts the most. She has won three of the last four Slams and is now 23-1 at majors this year. She has captured 11 career Slams and is seeking her fourth U.S. Open crown.
Against Clijsters, Serena leads 7-1 all-time and is a perfect 7-0 on hardcourts. But Clijsters is red hot, too, having won 11 straight matches in Flushing Meadows.
The semifinal match features an interesting historical footnote in that it will mark the first time since 1972 that two "defending champions" -- players who won the Open in their previous appearance -- will face off.
"I think she's always been able to step it up at the Grand Slams," Clijsters said. "I've seen her play here, and she has that face where she's like, 'Okay, I'm here to do business."
Whoever wins the Serena-Clijsters matchup will be the overwhelming favorite to win the tournament.
The other side of the bracket features three unseeded women, including 17-year-old sensation Melanie Oudin of Marietta, Ga. Oudin faces No. 9 Caroline Wozniacki of Denmark on Wednesday night in what is sure to be an electric atmosphere under the lights.
"I'm really watching Melanie's matches and she's doing very well," Serena told ESPN. "I'm cheering for her, 'Go Melanie.' She's such a good player.
"Finally I can stop answering questions about American tennis. Now she's the next big thing and she has another match that she can win. You can always win any match, so she can definitely do it. She has a lot of people rooting for her now."
Even Clijsters has jumped on the Oudin bandwagon.
"It's just fun to watch those young girls and just to see like even Oudin how freely she plays at big points," Clijsters said. "It's just so much fun to see how she just goes for her shots every time."
While Oudin is the new kid on the block, Serena and Clijsters are old friends who seem to genuinely like each other.
"She's such a nice person," Serena said. "I love her little daughter [Jada Ellie]. I'm just looking forward to the match."