ESPN 2008 US Open

NEW YORK -- By now, Venus and Serena Williams know all too well how it feels to set aside sisterhood for a couple hours and try to beat each other on a tennis court.

They know what it feels like to meet at a Grand Slam, what it feels like to win such a match, what it feels like to lose.

And they much prefer it when there's a major championship at stake. The all-Williams showdown, set up by their easy victories Monday at the U.S. Open, comes earlier this time.

This time, Williams vs. Williams is only a quarterfinal.

"It's so soon," Serena said. "You know, it's just disappointing to be so soon."

Both advanced through the fourth round without a challenge. The No. 7-seeded Venus dismissed No. 9 Agnieszka Radwanska of Poland 6-1, 6-3, before No. 4 Serena dispatched wild-card entrant Severine Bremond of France 6-2, 6-2 at night.

"Even the semis would have been better than the quarterfinals, but at least one of us will make it to the semis," Serena told the crowd during an on-court interview. "I've got probably the toughest match of the tournament coming up next, so I've got to be ready."

Some sisters make plans to go shopping together, say, or to catch a movie. These siblings keep running into each other at their sport's highest levels.

Venus beat Serena for the title at Wimbledon in July -- their seventh major title match -- and Wednesday will mark the first time they've squared off at consecutive Grand Slams since 2003.

Both have dealt with injuries and inactivity that stalled their dominance, but they are clearly are back at the height of their powers.

"The best part is that we're still here," Venus said, "going stronger than ever, in my opinion."

They've played 16 times as professionals, with each winning eight. That includes 10 meetings at major tournaments, with each winning five.

"I would love to have a winning record," Venus said. "I have a chance."

Because of the luck of the pre-tournament draw, they were placed in the same portion of the bracket in New York -- much to the disappointment of them, U.S. Open organizers and TV types. Even other players.

"For sure, it would have been better for the crowd if it was a final," Bremond said. "It would have been a very good final."

That certainly rings true: Serena has lost a total of 14 games through four matches at Flushing Meadows; Venus has dropped 15.

Of the eight women left in the tournament, only two have won a Grand Slam title -- Serena leads all active players with eight, and Venus is right behind with seven.

They won every U.S. Open women's singles championship from 1999 to 2002, meeting in the finals the last two years of that span -- it was their ascension that prompted the U.S. Open to move the women's final from Saturday afternoon to Saturday night. Since 2002, though, Serena hasn't made it past the quarterfinals here, and Venus has only reached one semifinal.

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"I just feel like, you know, we're both playing better and feeling better," Serena said. "We just had a turn in our careers. We're just playing the way we should play."

Also advancing Monday were No. 6 Dinara Safina, who defeated Anna-Lena Groenefeld 7-5, 6-0, and No. 16 Flavia Pennetta, who beat No. 32 Amelie Mauresmo 6-3, 6-0.

Venus faced what theoretically should have been an opponent to be taken seriously: Not only is Radwanska ranked in the top 10, but she won her only previous match against the elder Williams sister and she upset then-defending champion Maria Sharapova at last year's U.S. Open.

Radwanska needed 27 minutes just to claim a game this time and never came up with a reply for Venus' constant forays forward. Venus won the point 25 of 34 times at the net, and she put together a remarkable 33-11 advantage in winners.

"She was playing very aggressively, going to the net all the time. There was nothing I could do," Radwanska said. "She was too good."

Bremond offered essentially the same analysis after trying to slow Serena, who finished with a 24-10 edge in winners.

Asked to define her on-court sibling rivalry, Serena called it "classic" and "unique."

No argument there.

What about "difficult," given the prospect of trying to have success at a sister's expense?

"No. Not anymore," Serena replied. "Just another match. Another possibility for me."

A pep talk from coach Zeljko Krajan rescued an exhausted Safina's U.S. Open dreams earlier Monday.

"I didn't expect to win [Monday] because I was just so exhausted," Safina, who has reached six finals in her last seven tournaments, said in revealing that she almost did not make it on court for the match. "I finished the warm-up and I just said, 'I cannot push myself anymore.' I could not stop from crying.

"[My coach] said, 'We know that you're not a machine. Just go on the court and do whatever you can this day. If it's 20 percent left in your body, just give this 20 percent. Don't use another percent just throwing the balls around and shouting. Whatever you have, just try to concentrate and put it into the game.' So that's what I did today," she said.

Krajan's words of wisdom certainly paid dividends on Monday.

Groenefeld tried her best to rattle Safina when she stormed back from 4-2 down in the opening set to level at 5-5.

But that ended up being the last game the 141st-ranked Groenefeld won as Safina stayed calm and pounded down a string of sizzling groundstrokes to win in 75 minutes.

Safina said if it had not been for the influence of her Croatian coach, she probably would have been catching an early flight home.

"I've grown up a lot in the mind. A year ago I would not be able to do these kind of things," said Safina, who will next face Pennetta. "Maybe even the [third-round] match before against [Timea] Bacsinszky I would have already lost. But somehow I started to control better myself.

"You have a trust in the coach, so he understands me and I understand him, so that's why somehow it's easier that I can express my emotions. I didn't play my best but that I went through. This was the most important, because now I have one day off, and hopefully I can be 100 percent for my next one," she said.

The Russian is one of four players who could topple Ana Ivanovic, who lost in the second round, from the top spot next week.

Mauresmo had 14 double-faults and 40 unforced errors to help Pennetta reach her first Grand Slam quarterfinals.

"I think the conditions were pretty windy out there today," Mauresmo said when asked why she had struggled so badly on serve.

"It's definitely something that we will try to analyze and work on for the next tournaments," she said.

After an injury-hit year, Mauresmo had recently shown signs of the form that took her to the top of the rankings in 2006, but her serve was appalling from the start.

Once Pennetta had broken a second time to lead 4-3 in the first set, she was in total command.

"Of course I am very happy about this tournament," Pennetta said. "In the beginning I never thought I could get to the quarterfinals ... because I was so tired after [the Olympics] in Beijing.

"The first match was very tough for me. I didn't play my best tennis but I just tried to fight every point and keep going," she said.

Pennetta said she would need to be on top form to stand a chance against Safina, the runner-up at both the French Open and the Olympics.

"It's going to be tough for sure," she said. "She's a good player and she's in good shape. For sure, I have to play my best tennis to beat her.

"In this moment I just want to enjoy. Tomorrow we don't play, so I have one day off and just prepare for this match," she said.

Information from The Associated Press and Reuters was used in this report.