NEW YORK — Fifth-seeded Elena Dementieva reached the semifinals of the U.S. Open, beating No. 15 Patty Schnyder 6-2, 6-3 Tuesday in another one of tennis' most-played matchups.

While crowds at Flushing Meadows pressed around the practice courts to watch Serena Williams and Venus Williams warm up for their 17th career meeting Wednesday, Dementieva defeated Schnyder in their 17th contest.

"Every time it's different," Dementieva said, now 10-7 lifetime against her Swiss opponent.

After winning the Olympic gold medal and becoming a semifinalist at Wimbledon, Dementieva is on the best run of her life. She next plays the winner of the night match between No. 2 Jelena Jankovic and No. 29 Sybille Bammer.

Second-seeded Roger Federer and No. 3 Novak Djokovic were set to play by day and No. 8 Andy Roddick took on No. 11 Fernando Gonzalez at night. The men were trying to reach the quarterfinals.

Dementieva beat Schnyder for the fourth straight time, including three victories this season, in a pairing that started in 1997. Neither has won a Grand Slam, no match for the 15 combined major titles by the Williams sisters.

The Russian star made it to the final of the 2004 U.S. Open, but her often-shaky serve deserted her and she got swept by Svetlana Kuznetsova.

Dementieva did much better this time, putting 80 percent of her first tries in play. She also was much more steady, making only 14 unforced errors to Schnyder's 29.

"I think the serve was the key," Dementieva said.

Both Dementieva and Schnyder struggled to hit 110 mph with their serves. The speeds figure to be a lot faster when the Williams sisters meet.

Both sisters won Monday and head into this encounter all even in head-to-head matchups — 8-8 overall, and 5-5 in Grand Slam play.

"If I had a sister and she wasn't very good, then it would be just not really a big deal because I would beat her," Venus said Monday.

But Serena wouldn't change anything about their tennis prowess.

"I'm glad we're both pretty good at it, because I always use her," she said. "If I'm going somewhere and they give me a nice gift I'm like, 'Well, my sister, she's not here, but she would love that.' If she was no good then I wouldn't be able to do that. And I always keep it. She doesn't even know about it half the time.

"I guess maybe she'll know about it now."