Martina Hingis, fortified by the return of her mum, Melanie, and a few lessons on how to deal with the media, opened her challenge under the floodlights of the Arthur Ashe stadium in Flushing Meadows with a 61, 7-5 win over the Czech Republic's Kveta Hrdlickova, and then shed a little more light on her first-round defeat at Wimbledon and her tantrums at the French Open.

"We never broke up," Hingis insisted when questioned about her mother's absence when she lost to Australia's Jelena Dokic on number one court in June. "I just wanted to try it on my own, and it didn't work out. It happens to any family."

There was no doubt that Hingis was pleased to have her mother back in her corner. The traumatic events in Paris, where she lost the final to the now retired Steffi Graf, and then sobbed as her mother guided her back on court for the presentation ceremony, threw the 18-year-old Swiss prodigy so off balance that she was in no state to play at Wimbledon.

Since then she has had a holiday with her 23-year-old Swiss boyfriend and professional tennis player, Ivo Heuberger, bought a house in Florida, trained intensively, and won tournaments in San Diego and Toronto to lift her ahead of Lindsay Davenport of the US as the world's number one. "Everyone has to be taught something. I've grown up a little bit, and gained my first wisdom tooth. These things hurt, but I learned a lot," said Hingis, who won this title two years ago against Venus Williams, and was beaten in the final last year by Davenport.

Clearly her mother recognises the need for her daughter to have rather more independence in her private life, while insisting that on court Hingis needs to enjoy her tennis while adopting a professional and mature approach.

It is not beyond Hingis to win her sixth grand slam here, although this is not the way Richard Williams, the father of Venus and Serena, sees matters.

"I don't think nothing could stop my two girls. They run too fast for the others and they are a little too strong for them. The only person I see who can match their power is possibly Lindsay Davenport. But no one else," he said.

The sisters are on opposite sides of the draw and their father expects a repeat of the Lipton Championships in March when Venus beat her younger sister in the final.

"They've done a great job brightening up tennis, but to have them both in the final here would take it up the mountain and drip a little sweat on everyone," Williams added.

But Hingis, in the same half of the draw as Venus, has no intention of being left in the foothills.

Meanwhile, in the men's draw, world number one Pete Sampras was forced to withdraw because of a back injury.

Sampras, the top seed who was to play Russian Marat Safin in a first round match today, hurt his back while practising on Sunday.

The American, who captured his sixth Wimbledon crown this summer, was looking for his 13th grand slam title and first US Open championship since 1996.

It is the second time this month that Sampras has been foiled by injury. He hurt his hip going for an overhead smash in the semi-finals of the RCA Championships in Indianapolis against Vince Spadea and had to quit.

Sampras captured his first grand slam title at Flushing Meadows in 1990 when he beat Andre Agassi in a thrilling final.

Swede Mikael Tillstrom, ranked 130th in the world, takes his place in the draw and faces Safin.

"He suffered a very small herniated disc in his lower back," said Dr Brian Hainline, the US Open medical director. "It's not allowing him to move as he should. He has some pain, but he's completely normal otherwise.

"The good part is that we discovered it early. A large herniated disc could've jeopardised his future, so it's good we caught it early. We know that he always wants to play, so ultimately he made the decision on whether to play."

Sampras said: "For the past 48 hours I've been struggling just getting round my hotel room.

"Last night I had a few tests and they showed I've got a herniated disc, so obviously I've had to pull out of this event and I'll be out for some time.

"I'm fine sitting; it's any time I bend over that I'm very limited and it's very sore."

Sampras' departure could smooth Australian Pat Rafter's path to a third consecutive title.

Rafter, himself battling tendinitis in his shoulder, defeated Sampras in the semi-finals last year en route to his second straight title and was seeded to meet Sampras in the final four again.

As the Sampras drama unfolded off the court, seventh seed Todd Martin of the United States was dragging out the drama on court, finally triumphing 6-4, 6-3, 6-7 (2/7), 6-7 (5/7), 7-6 (7/3) over French qualifier Stephane Huet. Martin finally fired an ace to end the marathon after three hours and 59 minutes.

But Sampras remained the focus of the day.

"It's a shame," said unseeded American Jim Courier. "Pete would be here if he could at all be here. If the injury was going to get better, maybe he would try to sneak through."

Britain's Tim Henman became the first men's seed to crash out when he was destroyed 7-6 6-4 6-3 by Argentina's Guillermo Canas.

Henman, the world number five and seeded six, was way below his best against an opponent ranked 63 places below him in the world rankings.