Black Tennis Pros

The 20th showdown between the sisters ensures a finalist from the family Saturday. The Williamses have won eight of the past 11 Key Biscayne titles.

"I believe we are the best in the world," Venus said. "I enjoy playing Serena because we challenge each other the most."

"I'm always going to be up for V, because she's playing really well and always playing me super tough," top-ranked Serena said.

She advanced first Wednesday, overcoming a dismal start to beat unseeded Na Li 4-6, 7-6 (1), 6-2. Five hours later she was joined in the semis by No. 5-seeded Venus, who beat No. 26 Iveta Benesova 6-1, 6-4.

Venus leads the Williams family rivalry 10-9. She has won the past two meetings and has a 2-1 advantage at Key Biscayne.

"Playing her, it's like I have to automatically be on a different level, because she's already playing on a different level," Serena said. "Her balls are harder and her serve is way bigger. And it's super fun to hit these serves that are like 120 mph. It's frustrating but at the same time fun."

If Venus wins, she'll knock her kid sister out of the top ranking. Serena must reach the final to keep No. 2 Dinara Safina from overtaking her.

Venus has three titles in the tournament, but the most recent came in 2001. Serena seeks her sixth Key Biscayne title, which would break the record she shares with Steffi Graf.

The bid nearly ended against Li, who raced to a 5-0 lead while Serena looked lethargic in the 80-degree sunshine. Several times she declined to chase shots that seemed within reach.

"Wake up!" one spectator shouted.

"Maybe I was tired, but that's still not an excuse really," Serena said. "I definitely wasn't moving my feet at all. I just wasn't doing anything that made a lot of sense at all."

Midway through the first set, Richard Williams left his seat in the stands and positioned himself courtside near the baseline. He's the sisters' coach as well as their dad, and while he said little, he lifted Serena's spirits.

"I just felt like he was there really supporting, and I felt the support more when he was up close as opposed to in the stands," she said. "I just felt like I could take it up to another level."

She did, moving better and punctuating her shots with more emphatic grunts as the match slowly swung her way. There were no service breaks in the second set, but the unseeded Li failed to convert six break-point chances. The last came at 5-all, and Serena erased it with a service winner.

Li made things easy for Serena in the tiebreak by committing six unforced errors. As the third set began to slip away from Li, she vented her frustration by slamming a ball against the backstop on the far end of the court.

"I gave her the tiebreak," Li said. "I couldn't focus in the final set. After she won the second set, I didn't think I had a chance."

Li double-faulted on break point to fall behind 2-1, part of a stretch where Serena won 16 points in a row en route to a 5-1 lead. Serena closed out the victory with a service winner.

"The whole match is still an F," she said. "I'm glad to have gotten through."

Venus' victory was more straightforward, although she had a brief lapse in the second set when she fell behind 3-love. Smacking serves at up to 120 mph, she hit eight aces and won 21 of 26 first-serve points.

"I rely on my serve a lot -- sometimes too much," Venus said.

She's 15-1 this year, while Serena is 20-2 and won her 10th Grand Slam title in January at the Australian Open. Venus has been the more consistent Williams in the past week, while Serena managed the curious feat of reaching the semifinals despite losing five consecutive games three times in her past two matches.

"I need to be more consistent in my play," Serena said. "I don't have to be out there going three sets. That's what I think it tells me more than anything."

She improved her record at Key Biscayne to 51-5, with one loss since 2001 -- to her sister.