Nadia Petrova provided further evidence of the growing Russian strength in women's tennis when she defeated world number one Justine Henin-Hardenne 6-3, 6-2 in the fourth round of the U.S. Open in New York on Monday.

While Andre Agassi, Tim Henman and Lindsay Davenport made it a good day for the veterans by reaching the quarter-finals, the real drama came under the night lights as 14th seed Petrova, yet to win a WTA Tour singles title, knocked out the top seed.

"Of course it's my best win, in a Grand Slam, beating the defending champion," Petrova told reporters.

"I was a little bit doubtful that I could still pull this match out because, knowing her experience, I was thinking she would change something in the game and be more consistent, be in charge of the game. But I stayed strong until the end."

The 22-year-old Petrova now plays fellow countrywoman Svetlana Kuznetsova, the ninth seed. Russia has three players in the last eight, with Elena Dementieva their other quarter-finalist.

Anastasia Myskina became the first Russian woman to lift a Grand Slam singles title when she won the French Open in June. Maria Sharapova then made it back-to-back Russian victories when she triumphed at Wimbledon in July.

Earlier on Monday, 34-year-old Agassi set up a mouthwatering clash with men's world number one Roger Federer by trouncing Armenian Sargis Sargsian 6-3, 6-2, 6-2.

"I'm looking forward to it," Agassi said.

"There's nothing more you can ask than to play a big event against the best player. It's time to bring the best tennis.

"His (Federer's) forehand is just a nasty shot. He does a lot of things well and a few things really great, so it's going to be a tough match."

HERNIATED DISC

Australian Open and Wimbledon champion Federer, looking to become the first man since Sweden's Mats Wilander in 1988 to win three Grand Slams in the same year, received an unexpected day off when 16th seed Andrei Pavel pulled out with a herniated disc in his lower back.

When fifth seed Tim Henman woke up with a stiff back 10 days ago, the Briton did not think he would be able to play his first-round tie.

But, after surviving five-set battles against Ivo Karlovic and Michal Tabara, Henman celebrated his 30th birthday with a gutsy victory over Germany's Nicolas Kiefer.

The Briton looked in trouble when he trailed by a set and 3-1 but stormed back to win 10 games in succession to lead by two sets to one.

Kiefer snatched the fourth set but Henman was on top in the decider, leading 6-7, 6-3, 6-1, 6-7, 3-0 when the German retired with a suspected tendon injury to his right wrist.

"I felt that my game plan was pretty much spot on today," said Henman, whose semi-final appearance at the French Open in June was his first time past the last 16 at any Grand Slam outside of Wimbledon, where he has reached the last four on four occasions.

BAD BACK

"It's taken to have a bad back at the beginning of the tournament to sort of say to myself, 'You know, whatever happens, happens'. And if anything good happens, it's going to be a big, big bonus."

Henman will meet 22nd seed Dominik Hrbaty for a place in the semi-finals after the Slovakian came from two sets down to beat Belgian Olivier Rochus 2-6, 3-6, 6-3, 6-4, 6-0.

Fifth seed Davenport, 28, with four WTA Tour titles under her belt since her semi-final defeat by Sharapova at Wimbledon, edged out Venus Williams 7-5, 6-4.

Venus, seeded 11th, made 42 unforced errors before Davenport clinched victory on her fifth match point to reach the quarter-finals for the eighth year in succession.

"I definitely have worked harder since last November than I ever have, spending a lot of time in the gym," Davenport said.

"After that first win in Stanford (California, in July), it just seems like all the confidence came back to me after winning a close title match. I've just kind of gone with it since then."

Davenport will now play Japan's Shinobu Asagoe, the last unseeded player, who reached her first Grand Slam quarter-final with a 7-6, 4-6, 6-3 win over Greece's Eleni Daniilidou.

Kuznetsova reached the last eight for the first time when she ended the run of twice former Grand Slam champion Mary Pierce, 7-6, 6-2.