Wimbledon, England — The top seed stumbled, a former champion, Maria Sharapova, suffered an upset, and another former champion, Amelie Mauresmo, has faded since her glory days of just two years ago. All four top seeds, in fact, departed the women’s draw at Wimbledon in ignominious fashion this year. But the Williams sisters, the two best players at this tournament since Steffi Graf retired, are still here and on course for their first meeting in a Grand Slam final since Wimbledon 2003.

Venus moved into the semifinals yesterday with another patchy performance (6-4, 6-3 over veteran Tamarine Tanasugarn). She hasn’t lost a set so far, though she hasn’t played anyone ranked higher than no. 42 in the world, either (she has had one of the easiest paths to a major semifinal in her career). Serena played her best match of the tournament against Agnieszka Radwanska, a fast and steady 19-year-old from Poland (she won 6-4, 6-0). Serena started slow, but in the second set, which lasted 19 minutes, she lost a mere eight points and only two on her serve (she served 11 aces and hit a total of 27 winners against six unforced errors).

In tomorrow’s semifinals, the opposition won’t be terribly strong. Venus next faces Elena Dementieva, the soft-serving Russian who will play her first Wimbledon semifinal. Serena will take on Zheng Jie, a 24-year-old from China who usually shines in doubles (she won Wimbledon in 2006 with partner Yan Zi) but has used her crisp backhand and impeccable footwork to great effect these past two weeks, culminating in her victory yesterday against the ever-disappointing Nicole Vaidisova in the quarterfinals. Zheng is the first player from China, male or female, to reach a major semifinal in singles.

If (when?) the Williams sisters do meet in the final, there is more at stake than the Wimbledon title. Right now, Venus has been the better player at Wimbledon. She has four titles to Serena’s two. But Venus has never beaten Serena in a Wimbledon final. In 2002, Serena denied her sister the title; she repeated the performance in 2003. Sisterly love or not, Serena hopes to do the same this year if given the chance.

“I would never sit here and say she’s the favorite when I’m still in the draw,” Serena said. “What are you on?”

Serena, it’s clear, is playing for keeps. But will Venus?

In this sibling rivalry, little sister pretty much gets her way when the stakes are highest. In the early days of their careers, Venus got the better of Serena, winning five out of their first seven meetings, including the 2000 Wimbledon semifinal and the 2001 U.S. Open final. Serena soon lost any feeling of inferiority. After that U.S. Open final, Serena defeated Venus in six consecutive matches, including five in major finals (twice at Wimbledon and one each at the Australian Open, U.S. Open, and French Open). In those five finals, Venus won a total of two sets. She was older and a better athlete (no better athlete has ever played women’s tennis), but the world rightly considered her the second sister.

The Williams sisters’ father, Richard Williams, has often described Wimbledon as Venus’s event, and he considers Venus the favorite to win here (for years to come, in fact). In terms of talent, he’s correct. Venus is better built for Wimbledon, whose lawns are perfect for fast-running, long-limbed, powerful players with a knack for creative shotmaking. Serena has a lot of power and steadier strokes, but she’s slower around the court, generally less explosive (on serves and ground strokes) and much less comfortable around the net. Pit the two against each other at the height of their powers and Venus ought to win.

Is it a mental block? Venus would never say so. But she has generally been less than ruthless to her sister on the court; the same cannot be said for Serena. At Wimbledon this year, Venus has a chance to prove herself a more formidable champion than her sister at the most important tournament in the game. If she wins this title, it’s something the history books will remember for more than the title itself.

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Like the women, the men who remain at Wimbledon are a mix of titans — Roger Federer and Rafael Nadal, who are headed toward a third consecutive clash in the final — and surprises, none more so than Arnaud Clement, 30, and Rainer Schuettler, 32, who are best known as punching bags for Andre Agassi (both men lost to Agassi in straight sets in Australian Open finals). In between those highs and lows are four dangerous, and unpredictable, players: Marat Safin, Mario Ancic, Feliciano Lopez, and Andy Murray.

The match between Murray and Nadal is the one to watch. Murray nearly beat Nadal at the Australian Open two years ago and has the talent to do it again. He can attack the net. He can serve. He returns serve as well as anyone in the game. He’s also playing to a very partisan crowd that has shown Nadal much support the last few years, but will undoubtedly put the Spaniard second today. The question is, can Murray possibly play his best tennis for long enough? Nadal has improved with each match this tournament and is incredibly confident at the moment. He is the most determined man in tennis — too determined, it would seem, for Murray’s magic. It’ll be some party, though, if Murray proves the world wrong.

Mr. Perrotta is a senior editor at Tennis magazine. He can be reached at tperrotta@tennismagazine.com.