NEW YORK -- The streak of Sister Slams was under siege Friday.

In one U.S. Open semifinal, Venus Williams, hampered by a blister on her hand, trailed 0-40 in the 10th game of the third set. In the other, Serena Williams was down 5-2 in the second set, and later faced three set points.

Yet, with an air of inevitability, each sister leaned on their stinging serves to get out of trouble and set up another all-Williams major final.

Venus got past Amelie Mauresmo 6-3, 5-7, 6-4, taking the last five points with serves at up to 122 mph. Serena ran off the final five games to defeat fourth-seeded Lindsay Davenport 6-3, 7-5.

Not once in the 20th century did siblings meet to decide a Grand Slam title. It's about to happen at a third straight major, and for the fourth time in five majors.

"It's definitely very remarkable. It's a feat that's never happened before," said top-seeded Serena. "Growing up I figured, 'Hey, I want to be No. 1. I want to win Grand Slams.' Venus obviously had the same goals."

Venus beat Serena in the 2001 U.S. Open final, but the younger sister prevailed at the French Open and Wimbledon this year.

Venus has a 5-4 career edge against Serena, who has won their last three matches.

"They're dominating a lot more than I thought possible," said their father, Richard, who bounced around the stands at Arthur Ashe Stadium with four long-lens cameras slung over his shoulders.

And now it's about making various layers of history.

When the sisters go to the opposite ends of the court for Saturday's final, just as they do day after day when they practice together, each will aim for a rare feat:

-- Venus can become the first woman since Chris Evert in 1975-78 to win at least three straight U.S. Opens.

-- Serena can become the first since Steffi Graf in 1996 to win three straight Grand Slam tournaments in a year. She might be going for a true Grand Slam, if not for having missed the Australian Open with an ankle injury.

Whoever wins will be No. 1 in the rankings, a spot currently occupied by Serena. She wrested it from Venus at Wimbledon.

"Venus is definitely right there, if not a little bit ahead of me," said Serena, who won the family's first Grand Slam title at the 1999 U.S. Open.

Today's schedule begins with the men's semifinals. Pete Sampras will play Sjeng Schalken, followed by defending champion Lleyton Hewitt against Andre Agassi.