WIMBLEDON, England ? The Williams family has another Grand Slam final all to itself, this time with a twist:

Little Sis is No. 1.

Serena and Venus Williams both used unstoppable strokes and serves topping 115 mph to win lopsided Wimbledon semifinals Thursday and set up a third title match in the last four majors.

And Serena 15 months younger than 22-year-old Venus was assured of supplanting her atop the rankings no matter what happens in Saturday’s final. Serena never has been ahead of Venus.

“Just because I’m No. 1,” said Serena, who hasn’t dropped a set, “doesn’t mean I don’t want to win Wimbledon.”

She’d never been past the semifinals at the All England Club (losing at that stage to her sister in 2000), but was absolutely dominant in defeating No. 9-seeded Amelie Mauresmo 6-2, 6-1.

So was two-time defending champion Venus, who beat No. 6 Justine Henin 6-3, 6-2 in a rematch of last year’s final, but really was no match at all.

This all-Williams final follows those at September’s U.S. Open (won by Venus) and last month’s French Open (won by Serena).

“It’s just something that’s unprecedented,” Venus said. “Never seen before.”

Well, not quite. Back in 1884, at the very first major tournament, Maud Watson beat sister Lillian in the Wimbledon final. That was the only sibling-sibling Grand Slam final for 117 years.

The men’s semifinals were set Thursday: No. 1 Lleyton Hewitt vs. No. 4 Tim Henman, trying to be the first British champion since 1936; and No. 27 Xavier Malisse vs. No. 28 David Nalbandian.

Ticketholders can only hope those prove to be more competitive than the women’s final four did.

“Today,” Serena said, “I was immaculate.”

She showed no signs of being distracted by news that a German man accused of stalking her in five countries was released from custody after being arrested outside Wimbledon’s gates.

“I’m a strong person,” she said. “I try not to let things like that affect me.”

The 1999 U.S. Open champion had seven aces, including a 117 mph exclamation point to end the first set, plus 22 total winners to seven for Mauresmo, who beat Jennifer Capriati in the quarters.

Serena also won the point on 10 of 14 trips to the net.

During changeovers, she read notes jotted on a folded piece of paper. Mauresmo could have used some sort of cheat sheet explaining how to beat Serena, against whom she’s now 0-4.

“It’s a little bit sad for women’s tennis, but maybe it’s not the point of view for everybody,” the Frenchwoman said, referring to the sisters’ dominance. “People are going to get bored about it. It was already the final at the French Open. I can’t count how many people since yesterday told me, ‘We don’t want Williams final.”‘

At the start of the first Centre Court semifinal, it looked like a big upset might be brewing.

Henin, eight inches shorter than her 6-foot-1 opponent, broke serve in the opening game when Venus sent a forehand half-volley wide and dumped a backhand into the net.

The Belgian went up 2-0 by holding serve in an 11-minute epic of a game (“By then I was nice and warmed up,” Venus said). There were six deuces and two saved break points, one with a drop shot and the other with a volley on a sequence that ended with both players at the net.

At that juncture, it was as though Venus said to herself, “OK, enough kidding around.”

Starting at deuce in the next game, she smacked a forehand winner down the line and delivered a service winner at 115 mph to open a run of 12 straight points to go ahead 3-2.

That began a streak in which Venus won 10 of 11 games. Most impressively, she repeatedly melted Henin’s trademark backhand the best in the women’s game into another average stroke.

Venus had 10 winners from the baseline and an unusually high-for-her 11 at the net. She’s won 20 straight matches at Wimbledon and one more would make her the first woman with three consecutive titles since Steffi Graf in 1991-93.

“She was too strong, too good,” said Henin, who lost the 2001 final in three sets. “She didn’t make a lot of mistakes. She didn’t let me play. She was so aggressive, so powerful.

“What could I do?”

The elder Williams’ serve, court coverage and power off both wings can be countered by only one woman right now: her sister. Venus is 0-2 vs. Serena in 2002 and 41-3 against everyone else.

Already owners of a career Grand Slam in doubles, they went out after their singles victories and beat Laura Montalvo and Elena Tatarkova 6-2, 6-2 to reach the quarterfinals. Venus and Serena slapped palms between points, and shared a giggle when Venus whiffed trying to return a serve.

The siblings are never quite so at ease on opposite sides of a net.

Their eight pro encounters (Venus has won five) have been lackluster. In the French Open final, for example, they splattered shots the way Jackson Pollack used paint, producing 101 unforced errors, 14 double faults and 13 service breaks.

Maybe it’s nerves, maybe it’s tough to want to outclass kin, maybe they just know each other’s games too well (they practice together, after all).

No matter the quality of play Saturday, though, a Williams will have won seven of the past 12 majors.

Their father and coach, Richard, back home in Florida, can be proud knowing that what once seemed like outlandish predictions his daughters would be ranked 1-2, they would win a passel of majors, Serena eventually would be ranked higher have come true.

“It’s tough enough to raise one great player. That’s why I appreciate my parents,” Serena said.

“They’ve really done not one, but two.”