Flushing Meadows witnessed another curiously unsatisfying episode of the Venus and Serena Williams [Images] story on Sunday.

This time Venus enjoyed the happy ending, winning 7-6, 6-2 to level their head-to-head record at seven-all and move through to the US Open [Images] quarter-finals.

Also Read Sharapova stops Sania Steffi inspires me: Agassi

There the Wimbledon [Images] champion will face in-form Belgian fourth seed Kim Clijsters [Images], who embarrassed Venezuela's Maria Vento-Kabchi 6-1, 6-0.

They were joined in the last eight by Russian top seed Maria Sharapova [Images], who produced her best tennis of the tournament to beat hard-hitting Indian Sania Mirza [Images] 6-2, 6-1 and reach the quarter-finals for the first time.

Men's defending champion Roger Federer [Images] fended off tenacious Belgian Olivier Rochus, winning their third round match 6-3, 7-6, 6-2 despite lacking some of his usual fluency.

Third seed Lleyton Hewitt [Images] was stretched to limit by American Taylor Dent in a five-set thriller but won to stay on course for a semi-final showdown against Federer.

As so often in the past, the meeting of sport's most famous siblings was a strangely muted, messy affair. Venus won a protracted first set 7-5 in the tiebreak and after that Serena's inferior physical condition ultimately counted against her.

"Weird, awkward, bizarre," were the words Serena chose to describe the unusual early round meeting with her older sister, who like her is a twice former US Open champion.

The last time they played at a Grand Slam Venus was stricken with an abdominal strain and lost a low-key Wimbledon final to Serena in 2003. This time eighth seed Serena's left knee and ankle problems came home to roost.

"It was super strange for sure," said 10th seed Venus, who contributed 29 of the 59 unforced errors that littered the match.

"It was tough but I don't think Serena had her best [game] today.

"Serena is so tough she'll never admit to anything...but to me it looked like it [she was not fully fit]. So I guess I was a lucky girl."

Mirza is probably the only women's tennis player who can rival Sharapova's global marketing potential thanks to her enormous Indian fanbase and she also has a forehand of Sharapova-like proportions.

The Russian was at times out-hit by her fellow 18-year-old in the first set but too many unforced errors by the first Indian woman to reach the fourth round of a Grand Slam proved to be her undoing.

"I'm playing pretty well," said Sharapova, the 2004 Wimbledon champion. "I know it's going to get tougher and tougher from here."

Mirza said: "There were a lot of games that I could have taken but I had fun out there. In my first US Open I couldn't have asked for any more."

INDOMITABLE SPIRIT

Sharapova will play compatriot and ninth seed Nadia Petrova in the last eight, a repeat of their Wimbledon quarter-final this year which Sharapova won in straight sets.

Petrova, who has never won a tour title, reached the quarter-finals for the second consecutive year with a 7-6, 7-5 victory over temperamental 16-year-old Czech Nicole Vaidisova.

Federer almost lost his first set of the tournament when he trailed 4-1 in the second set tiebreak against Rochus, his former junior doubles partner.

The Swiss will play German Nicolas Kiefer, who beat Arnaud Clement of France [Images] in four sets, in the last 16. Federer beat Kiefer in four sets on his way to winning Wimbledon this year.

"I expect a tough one," said the top seed. "He's been improving the last few months."

Hewitt eventually quelled Dent 6-3, 3-6, 6-7, 6-2, 7-5 on a breezy Arthur Ashe Court.

"It was an extremely tough match," admitted the Australian. "I really had to earn it. I felt like there were a lot of areas of my game that weren't quite clicking today."

The 2001 champion will play Slovakia's Dominik Hrbaty in the fourth round. Hrbaty, seeded 15, beat David Ferrer of Spain in four sets on Sunday.

Jarkko Nieminen became only the second Finnish man to reach the fourth round at a Grand Slam event, and the first at the US Open, when he beat Belarus's Max Mirnyi 6-3, 7-6, 3-6, 6-3.

Spain's Fernando Verdasco is the Finn's fourth round opponent. He fought out a five-set win over Serbia and Montenegran teenager Novak Djokovic [Images].

Davide Sanguinetti became the first Italian to reach the last 16 of the men's singles for 11 years after an epic four-hour, 24-minute 6-3, 4-6, 6-7, 7-6, 7-6 win over Thailand's Paradorn Srichaphan [Images].

• Complete tennis coverage
• All you want to know about Sania Mirza