MASON, Ohio — Kim Clijsters is turning Cincinnati into her kind of town.

The defending U.S. Open champion reached the semifinals at the Cincinnati Open on Friday, beating Italy's Flavia Pennetta 7-6 (6), 6-4 in oppressive afternoon heat. The fourth-seeded Clijsters will face Serbia's Ana Ivanovic.

Clijsters is the highest remaining seed. Five of the top eight were eliminated on Thursday. Serena and Venus Williams dropped out with injuries before the tournament began.

That left center court to Clijsters, who seems to like the place.

Clijsters returned to tennis in Cincinnati last year, reaching the quarterfinals after a two-year break to start a family and get recharged. The 27-year-old Belgian reached the quarterfinals in Cincinnati and found her touch. A few weeks later, she won the U.S. Open.

This year, she took a break from tournament play after Wimbledon and arrived in town hoping to use Cincinnati as a springboard again.

So far, the hard courts have been agreeable.

Clijsters passed her toughest test of the week, making a few more shots than Pennetta in a match close throughout. She hit a service winner to go up 7-6 in the tiebreaker, and Pennetta sailed a forehand wide to settle the sweaty first set.

Clijsters went to her seat and squirted cold water over her hair, trying to get a little relief. On-court temperatures have registered 120 degrees the past couple of days, with oppressive humidity that made it tough to breathe after long points.

Pennetta broke her in the second set to go up 3-2, which only seemed to make Clijsters more determined. She broke the Italian right back and served out the one-hour, 48-minute match on a court that felt more like a griddle.

The heat had a lot to do with how the day's first match turned out.

Down 5-1 in the opening set, Russia's Anastasia Pavlyuchenkova started to think about doing better in the second set. Turned out the first one was far from over.

Taking advantage of a heat-drained opponent, the 19-year-old Russian rallied for a 7-5, 3-6, 6-1 win over Yanina Wickmayer, extending one of the best stretches of her career.

Her opponent used so much energy getting ahead 5-1 in the first set that she began feeling the strain. Her legs got a little shaky. Her game fell apart.

"I started off really well in the first set, got really tired after that," Wickmayer said. "And she came back and put up a great fight."