ESPN 2008 US Open

NEW YORK -- They have been trading shots for more than two decades, going back to their earliest public-court battles in Compton, Calif.

Today, they find themselves in the backstretch of their careers. It's impossible to know how many major titles are left, but it's safe to say that at 28 and 26, respectively, Venus and Serena Williams are feeling a sense of urgency.

They consistently remain the best and biggest hitters in the women's game. After a series of sluggish, emotionally flat contests through the years, the sisters finally have learned to channel their familial feelings and feel free enough to play the swift and emphatic power tennis that made them champions.

It was only a Wednesday night U.S. Open quarterfinal, but Serena-Venus XVII felt like a championship match.

Venus earned an amazing total of 10 set points, any one of which would have forced a third set, yet failed to win even one. Serena was a 7-6 (6), 7-6 (7) winner in a tremendously taut match that consumed 2 hours and 25 minutes.

"At 5-3, 40-love [in the second set], I thought, 'Wow, these should be match points -- and they weren't,'" Venus said. "I felt like I was always in control.

"I'm a very good closer. I've never had a match like that in my life. I guess there's always a first."

Serena now faces Russia's Dinara Safina, the Olympic silver medalist, in Friday's semifinal.

"She made a couple of errors," Serena said about those 10 set points, "and it was really luck for me, because she never makes those errors."

Before the match, Serena said playing Venus gets easier every time they play. Perhaps. But after Venus winged an errant forehand and saw her challenge denied, Serena's victory smile faded as soon as she saw her sister approaching the net. When Venus first focused on Serena, however, her frown turned to a smile.

"I try not to look at her, so I don't feel sorry," Serena said.

Playing on the grass, her best surface, at Wimbledon two months ago, Venus looked invincible, beating her little sister in straight sets. Serena was uncharacteristically tentative, losing 11 of 13 break points.

"I definitely managed my emotions a lot better," Serena said. "I felt like I really got negative at Wimbledon and lost any chance I might have had. When she was up, I got relaxed."

Here on the blue Deco Turf II, the court that best suits Serena's game, Venus' eyes carried a look of concern from the beginning. On grass, where the ball skids low and defense is more difficult, Venus' higher-risk game is rewarded. On hard courts, the ball bounces higher, rallies seem to last longer and her margin for error is less.

Venus consistently served eight miles per hour faster than Serena and took bigger cuts on her ground strokes, recording 36 winners but making 45 unforced errors, a net of minus-nine. Serena was a more economical minus-four. While Venus pressed the attack, coming to the net 32 times (winning 25 points), Serena was nearly as aggressive, winning 16 of 23 points when she came to the net.

On those big points, Serena made the decision to take a little off the ball, building a degree of safety into even her stronger shots. Ultimately, this was the difference in the match.

Afterward, Venus said she thought she would have prevailed over any other player. For her part, Serena felt like she should have been holding the silver trophy after the high level of tennis played.

When the sisters have met before an event's semifinals, the winner has never gone on to win the title. It's happened four times. Maybe they invest so much psychic energy in the sibling struggle, they don't have much left for the rest of the field.

Serena won the family's first Grand Slam here, back in 1999 at the age of 17. Venus returned the favor, winning the U.S. Open in 2000 and 2001, and Serena came back to win in 2002. Since then they have gone 0-for-5.

With 2006 and 2007 U.S. Open champions Maria Sharapova (injury) and Justine Henin (retirement) out, and No. 1 and No. 3 seeds Ana Ivanovic and Svetlana Kuznetsova (2004 champion) out of the draw, that losing streak may come to an end.

Serena, who has been working hard to get in shape for about a year now, has an additional motivation. Two more victories would vault her back to the No. 1 ranking she hasn't held in more than five years.

"Honestly, I'd really rather win the tournament, with or without the ranking," she said.

"Believe me, I'm going to be No. 1, sooner or later."

Greg Garber is a senior writer for ESPN.com.