The Belgian lost her serve seven times and racked up 47 unforced errors during her 6-2, 5-7, 6-2 defeat of former Israeli soldier Tzipora Obziler and she will need a dramatic improvement if she is to advance deep into the tournament.

American trio Andre Agassi, Lindsay Davenport and Venus Williams together with Russia's Maria Sharapova all experienced a few hitches before rolling on, although French Open champions Gaston Gaudio and Anastasia Myskina were sent packing.

Double Olympic gold medallist Nicolas Massu also came down to earth with a bump, losing a five-set thriller to Sargis Sargsian in what, at five hours 10 minutes, was the second longest match in US Open history.

To make matters worse for the 10th-seeded Chilean he failed to convert a matchpoint at 6-5 in a fourth-set tiebreak and received a game penalty at the start of the deciding set after being warned about his behaviour.

Earlier Henin-Hardenne, who returned from a virus to win Olympic gold, cruised through the first set against 31-year-old Obziler before her game began to disintegrate.

Obziler, who had never got beyond the first round of qualifying in four previous visits, seized her chance to level the match before Henin-Hardenne clinched victory in just over two hours.

"I was worried at the end of the second set, I was in a hurry to finish it," Henin-Hardenne said.

"She was running all over the court and I had to work very hard."

Twice champion Agassi briefly looked in trouble against Germany's Florian Mayer when he lost the second set 6-2 having edged a tight opener 7-5.

Normal service was resumed when the 34-year-old sixth seed won the third 6-2 and Mayer retired early in the fourth with a leg injury to save Agassi further exertion.

"You never expect that, I don't know what his injury was but it didn't look good. I still felt like I had 40 good minutes left in me to finish the match though," said Agassi, who clocked up his 69th win at the US Open.

With many fans snagged in traffic caused by the arrival of President Bush to Madison Square Garden for the Republican Party convention, Davenport's second round match against Spain's Arantxa Parra Santonja was played in a half empty Arthur Ashe Court.

But the American fifth seed recovered from a wobbly start to win 6-4, 6-2 and stretch her winning streak to 19 matches.

"It took me a while to get going and I definitely have to try to do something to get a quicker start in the next match," said Davenport, who will face dangerous Russian Elena Bovina.

There were few empty seats later on, however, as Wimbledon champion Sharapova produced a mixed bag of crunching winners and sloppy errors in her 6-0, 6-7 6-1 victory over fellow Nick Bollettieri graduate Jelena Jankovic.

"I don't think I'm playing the best tennis but you don't want to be playing your best in the first two rounds," said Sharapova, who now faces Mary Pierce.

Eleventh seed Venus Williams found herself 4-1 down against Indian-born American qualifier Shikha Uberoi before hitting back to win 11 of the next 13 games for a 7-5, 6-1 victory.

Men's ninth seed Gaudio ripped his shorts apart in disgust during his four-set defeat by Sweden's Thomas Johansson, while women's fourth seed Myskina was humbled 7-6, 6-3 by fellow Russian, 17-year-old qualifier Anna Chakvetadze.

"That was a pretty bad match for me," said Myskina, who became the first Russian woman to win a Grand Slam at Roland Garros this year.

"I had nothing. I didn't want to run, didn't want to fight, I didn't want to do anything. But that's life."

Britain's Tim Henman led a cluvictory over Australia's Nicole Pratt.