The US Open lost one of its top attractions when holder Maria Sharapova [Images] was beaten 6-4, 1-6, 6-2 by Polish teenager Agnieszka Radwanska in the third round on Saturday.

Sharapova lost only two games during her first two matches at the tournament but never got on track against 18-year-old Radwanska, committing an uncharacteristic 49 unforced errors.

"You've got to give her a lot of credit for finishing the match and winning it," the second-seeded Sharapova told reporters.

"A lot of girls in her position on a big stage in a big stadium against a top player sometimes get a little nervous."

Roger Federer [Images], aiming for a fourth consecutive US Open title, defeated hard-hitting rookie John Isner 6-7, 6-2, 6-4, 6-2.

Federer had only 11 unforced errors against the American wildcard who has been impressive since joining the tour in July.

"It's so hard to play against players like him, you just hope he's not going to keep serving aces," said Federer, who watched nine of Isner's 18 aces fly by in the opening frame.

"It was unbelievable how he served in the first set. But I started to get a read of it a bit in the second and third."

Russian fourth seed Nikolay Davydenko reached the fourth round with a 7-5, 6-0, 7-5 victory over Spaniard Nicolas Almagro, while number five and 2003 champion Andy Roddick [Images] blasted 19 aces to defeat Sweden's Thomas Johansson 6-2, 6-2, 6-0.

Sixth-seeded American James Blake also advanced beating Austrian Stefan Koubek 6-4, 3-6, 7-6, 6-1 to end Day Six of the tournament at Arthur Ashe Stadium.

On the women's side, number seven seed Nadia Petrova of Russia [Images] committed 29 errors during a 6-4, 6-4 upset loss to 18-year-old Hungarian Agnes Szavay.

Fourth-seeded former champion Svetlana Kuznetsova and sixth seed Anna Chakvetadze [Images] kept Russia's title hopes alive. Kuznetsova beat Spain's Anabel Medina Garrigues 6-3 6-1, and Chakvetadze defeated Sania Mirza [Images] of India 6-2 6-3.

EARLIEST EXIT

Martina Hingis's [Images] 10-year anniversary since winning the US Open ended in disappointment when she lost to Belarusian Victoria Azarenka 3-6, 6-1, 6-0 in a third-round match.

Another favourite to fall was 13th seed Nicole Vaidisova of Czech Republic, a 6-4, 3-6, 7-6 loser to Israeli Shahar Peer in the first women's match of the tournament to be decided in a third-set tiebreaker.

But the buzz around the National Tennis Center was the unexpected defeat of Sharapova, her earliest grand slam exit since losing in the third round at Flushing Meadows in 2004.

Sharapova produced 12 double-faults, unable to cope with swirling winds in Arthur Ashe Stadium. With her tournament life on the line in the final set, the Russian made 20 errors.

"There's no excuses," said Sharapova. "It's not like today I stepped out on the wrong side of the bed or I did something differently.

"I'm going to have these types of days where I might be up a break in the third set but it just doesn't go my way."

The 30th-seeded Radwanska served just two double faults but landed only 57 percent of her first serves. She conceded that many of her key points were gifts from Sharapova.

"I had problems with my serve but I think she made many mistakes and double faults so I think she was a little bit nervous," said the 18-yer-old Radwanska.

Radwanska had lost eight consecutive games when she fell behind in the final set 2-0. But she rebounded with a six-game streak of her own to close out the two-hour, four-minute match and set up a round-of-16 tilt against Peer.

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