WIMBLEDON, England - One has a quick smile, bubbly personality and Grand Slam title to call her own.
The other is a fearsome competitor, but for her promise has yet to win a major tennis prize.
Williams vs. Williams is Wimbledon's main event, the family gathering and historic tennis slugfest televised 'round the world. Not since Maud Watson defeated her sister Lilian in the first women's final in 1884 have two sisters met so late in Wimbledon's championships.
The match is overshadowing the other women's semifinal between reigning champion Lindsay Davenport and Jelena Dokic.
It's dominating the talk of tennis insiders trying to figure out which sister will win.
It's even causing a flurry among Britain's bookmakers, who have installed 18-year-old Serena Williams, the reigning U.S. Open champion, as a slight favorite over Venus, 20.
In eight meetings among sisters during the 32-year professional era, the older sister has won every time, including Venus, who beat Serena at the 1998 Australian Open.
Lifetime, Venus Williams enjoys a 3-1 edge over Serena.
The sisters warmed up for their showdown by bashing around a legend in yesterday's doubles. The Williamses didn't just overpower Martina Navratilova and Mariaan de Swardt, 4-6, 6-2, 6-1, they managed to take turns swatting Navratilova with tennis balls.
Serena slammed her on the left shoulder.
Venus clunked her on the head.
Afterward, they talked admiringly about a player who has won nine Wimbledon singles titles.
"She used to be my favorite player," Serena Williams said. "When I was younger, I used to admire her."
Navratilova, 43, didn't mind absorbing hard knocks, and later calmly analyzed the contrasting styles of two sisters who may yet dominate the women's game.
"They have the capability of taking it [women's tennis] another step," Navratilova said. "They just haven't gotten there yet. With their size, they're just so big."
In her day, Navratilova, 5 feet 7, was the most intimidating women's player on tour. In this era, she'd be one of the smaller stars. She looks up to both the Williams sisters: Serena is 5-10 and Venus 6-1.
"Serena's shoulders are about that wide," Navratilova said, stretching her arms. "I thought I was big; I'm like a pip-squeak standing next to them. They're imposing. If they put it together technically, we could see them in the finals for a lot of years to come, if they commit themselves to that, if they want to stay around."
In her prime, though, Navratilova said she had no doubt how she would have done against the sisters.
"I would have beaten them the way they're playing right now," she said. "They haven't reached their prime right now."
She said Serena's second serve was easier to return than Venus', but that Serena "just comes at you a little more physically."
"I still say Serena would have a slight edge," she said. "I think she's hitting the ball deeper, and I think she's a little more comfortable coming in and attacking a little more effectively. Venus, I still feel like she's coming in because she's supposed to, whereas Serena is coming because she wants to."
Six-time Wimbledon champion Pete Sampras sought to avoid taking sides in the family match.
"It should be entertaining and tough for them to play each other," he said. "I'll take a Williams. I don't know which one. Maybe the younger one."
Andre Agassi agreed that Serena is the likely favorite.
"I just think those two girls are a level of athlete above all the other girls," he said. "Even if they're not playing well, they're still athletic enough to present a bunch of problems. Fundamentally speaking, I think Serena is a better player than Venus. I think her second serve is better. I think her forehand is better. I think she's a sounder mover. She doesn't jeopardize her body with long strides.
"You've got to favor certainly one of them to win the tournament," he added. "I don't know. It's always a psychological match up. I can't even imagine what it's like playing your sibling."
The sisters sought to downplay the hype.
What did they intend to do in the buildup?
"Nothing," Venus Williams said.
They want to take this match like any other, they said, warming up together and then going on to the court.
They're not sure what advice they'll receive from their father and coach, Richard Williams.
"At this point, my dad will probably say, 'Here's the balls, go practice,' " Venus Williams said.
It's not even clear if he'll even watch the match. After first saying that he intended to go to a funeral - it was actually held yesterday - he said he would spend the match working on a computer cooking up new business deals.
"I don't think he feels awkward," Serena Williams said. "I think, if anything, he's excited because two of his players are in the semifinals. What more could you want besides two of his players to be in the finals?"
It's hard match to figure. Rarely in tennis do family and history mix on such an important stage.
Yet for all that is at stake, a place in the final, a chance to win Wimbledon, Serena Williams sought to put the match in perspective.
'Tennis is just a game," she said after winning in the quarterfinals. "Family is forever."