WIMBLEDON, England -- One prematch glance at the data displayed on those new digital scoreboards at staid, old Wimbledon provided a persuasive case for why Venus Williams might be considered the woman to beat.

The entry under career record at the grass-court Grand Slam: "55-7." The listing of her best result: "WINNER 2007, 2005, 2001, 2000."

Yet another reason to like the American's chances: The way she served during the ensuing 6-4, 6-3 quarterfinal victory yesterday over Tamarine Tanasugarn -- smacking eight aces, saving nine of the 10 break points, tying her Wimbledon record with a 127 mph delivery.

That extended Williams' winning streak at the All England Club to 12 matches, including 19 sets in a row. Nonetheless, at least one person who knows a thing or two about tennis and a thing or two about Venus Williams flatly rejected the notion that she's the favorite: Serena Williams.

Asked after her own impressive quarterfinal victory -- 6-4, 6-0 against 11th-ranked Agnieszka Radwanska -- whether her older sister should be considered the likeliest champion, Serena shot back: "I would never sit here and say she's the favorite when I'm still in the draw. What are you on?"

Rather than a sibling rivalry, that response perhaps reflects nothing more than the sort of competitive drive that helped the younger Williams win eight Grand Slam singles titles. That haul includes the 2002 and 2003 Wimbledon championships, each time concluded by beating her sister.

One more win apiece, and they'll reprise the all-in-the-family final tradition Saturday. In tomorrow's semifinals, Serena will face 133rd-ranked Zheng Jie, who became the first Chinese player to reach the semifinals at a major tournament by upsetting 18th-seeded Nicole Vaidisova 6-2, 5-7, 6-1.

Venus next plays the highest-seeded remaining woman, No. 5 Elena Dementieva, who beat No. 21 Nadia Petrova 6-1, 6-7 (7-6), 6-3.

Zheng is the first wild-card entrant to reach the women's semifinals at Wimbledon; only one woman ranked lower has made the semifinals at any Grand Slam.

Against Radwanska, Serena hit 11 aces, including four in one game while pulling even at 3 in the first set. On the last of those, Radwanska lunged and whiffed, then grimaced at her racket.

"It's too much, you know," Radwanska said.

While Serena mixed in flat 120 mph serves with spinning, kicking changeups, Venus stuck with the hard stuff against Tanasugarn.

"I have a lot of power, so it helps," Venus said. "Definitely, the power helps."

Neither Williams has dropped a set during the tournament, and their seedings -- Serena is No. 6, Venus No. 7 -- certainly seem to have been miscalculated. It's the first time at any Grand Slam in the 40-year Open era that none of the four top-seeded women reached the quarterfinals, making the path even smoother for the siblings.

There hasn't been a Williams vs. Williams final at a tournament since 2003 at the All England Club.

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