The top-seeded Hingis was scheduled to play her fourth-round match against 11th seed Sandrine Testud of France following boyfriend Magnus Norman's third-rounder on Grandstand court on Sunday.

The third-seeded Norman, however, played the longest match of the U.S. Open at four hours, six-minutes, barely surviving a heart-stopping 3-6, 4-6, 7-6 (7-5), 6-4, 7-6 (11-9) encounter with Belarussian Max Mirnyi.

A long rain delay made the time it actually took to finish the match six hours, 26 minutes and left a nervous Hingis in the locker room, more worried about Norman's results than her own upcoming match.

"I had to watch it," said Hingis, whose own match was suspended by rain after the first set on Sunday. The world number one Swiss came back on Monday to complete a 6-2, 6-1 victory. "I was like waiting and waiting. He was two sets down. In a way I was like, he's going to finish this match up somehow.

"Great win for him, to pull it out, four match points."

Hingis did admit she was starting to get a little unhappy about the delay, eventually finding herself talking to the TV screen at Norman, saying: "Come on, get it over."

After the win, Norman said he suspected Hingis might not be too enamored with him for keeping her waiting.

"She'll probably kill me when I get home," he said, laughing.

Norman is known for his workaholic nature, often spending up to six hours training when not at a tournament.

Hingis had a firsthand peek at his work ethic this summer when he spent a week with her at the Saddlebrook Resort, the same community that Monica Seles and Jennifer Capriati call home.

"It was nice seeing him, actually," said Hingis, who will be looking for an 11th victory in 13 matches played against Seles in the quarters. "We both were practicing and working out together. It's like I never had that before. You go out there, practice, you see someone else working, too, who's number one and two in the world.

"That gives you like a little excitement that you really want to be out there, you still see each other."

A five-time Grand Slam champion, Hingis believes Norman has the potential to bring home a Grand Slam trophy for himself.

Norman reached his first ever Grand Slam semifinal at this year's Australian Open, and followed that by reaching the finals at the French Open, falling to Gustavo Kuerten.

"I don't know how well I know him," Hingis said of Norman. "It's been a short time. Not like we've been together forever.

"I think he has a great chance. He's really focused. He wants to win this Grand Slam very bad, as everyone else wants to.

"I want to do well, too," added Hingis, who hopes to claim her second U.S. Open trophy and first Grand Slam title since the 1999 Australian Open.