NEW YORK -- Venus Williams hit bottom, so to speak, when she double-faulted three times in one game, whiffed at an overhead, stomped to her chair, missed the seat and plopped to the court.
The sheer indignity of it all only compounded the frustration she felt throughout her match Tuesday against a relentlessly net-charging Nathalie Tauziat.
Yet even on her worst day, Williams still was good enough to win, 6-4, 1-6, 6-1, and extend her tour-leading streak to 24 matches as she moved into the semifinals of the U.S. Open.
Williams, seeded No. 3, will have to play far better to beat No. 1 Martina Hingis on Thursday.
Hingis knocked out Williams in the semis last year before losing to Serena Williams in the title match, and has been the most dominant woman in the tournament so far this year. She reached the semis Tuesday night with a 6-0, 7-5 rout of No. 6 Monica Seles, and has yielded only 15 games in five matches without dropping a set.
Williams had not lost a set in the tournament, and had dropped only three sets in her winning streak. But after a listless first set against Tauziat, and a sleepwalking second set filled with unforced errors, she powered up her serve and groundstrokes a notch to wear down the small but spirited Frenchwoman.
"You walk off against her and you don't have the impression you played a tennis match," Tauziat said. "You feel as if you've been in a tag-team wrestling match or a boxing bout, but not tennis. She just bangs away. It's in, it's out, it's a double-fault, it's an ace. You just never know what's coming."
Half the time, Williams also didn't know what was coming off her racket as she sprayed her serves in sundry directions and whacked groundstrokes wildly. She had seven aces and 10 double-faults. She was too aggressive or too tame, sometimes reaching for balls that would have flown long, or hitting shots safely down the middle.
"A lot of times I was rushing when I really could have just taken my time and hit some nice passing shots or some lobs," she said. "I never get upset when I'm playing, but today ... it was very strange.
"I thought I had quit playing tennis like that. It's been a little while since I played a match like that. I can't accept these things."
She had not played so badly in any other match during her winning streak from Wimbledon to here, she said, and had not played a worse set during that stretch than the second one against Tauziat.
Williams didn't blame her problems on the gusting wind or the fatigue of playing day and night for the past four days because of the rain delays and her singles and doubles schedule with her sister, Serena. Rather, she chalked it up to just one of those days best forgotten.
Her frustration was epitomized by her misadventure with her chair after she was broken on serve in the third set. She had taken control of the set by sweeping the first four games but then came unglued again, double-faulting three times, completely missing the ball on an overhead swing, and netting a backhand at break point.
Pouting and stomping her feet, she marched to the sideline on the changeover, missed the seat as badly as she had missed the overhead, and fell awkwardly. Tauziat and spectators laughed, but Williams didn't see any humor in it.
"I was just angry," she said. "I just couldn't see."
But when that moment of blind rage passed, Williams recovered her poise enough to break the tiring Tauziat one more time and close out the match with only two unforced errors in the last two games.
"Finally, physical ability was the decisive factor," Tauziat said, "because right at the end I hit volleys that nobody else would have got to, and Venus was there all the time."
But Tauziat also thought she had exposed Williams' vulnerability a bit.
"I think if she (is to) win the tournament, she needs to improve her level," she said. "I don't think she is going to win if she plays like this."
In men's matches, No. 14 Nicolas Kiefer knocked off No. 3 Magnus Norman 6-7 (3), 6-1, 6-3 to set up a quarterfinal match against No. 6 Marat Safin, a 6-1, 6-2, 6-2 victor over Juan Carlos Ferrero.
Unseeded Swede Thomas Johansson also reached the quarters, beating Wayne Arthurs 6-4, 6-7 (7), 6-3, 6-4, and will play the winner of the Todd Martin-Carlos Moya night match.
Norman's loss left No. 4 Pete Sampras as the highest seed remaining on the men's side of the Open draw. Top-seeded Andre Agassi and No. 2 Gustavo Kuerten were eliminated in the first three days of the season's final Grand Slam event. No. 5 Yevgeny Kafelnikov also departed in the first week.
Norman had courted trouble two days ago when he dropped the first two sets but battled back to defeat Max Mirnyi in a rain-delayed match that went from day to night at the National Tennis Center.
After losing the first set this time, Norman managed to win the tiebreaker in the second. But Kiefer dominated after that, taking advantage of 59 unforced errors that kept Norman in trouble.
It was a disappointing ending for Norman, who could have taken over the No. 1 spot in the ATP Champions Race by reaching the semifinals. Enjoying the finest year of his career, he came to the Open with 58 wins this year, more than any other player on the Tour.
Kiefer seemed unimpressed. The German, who has never lost a round-of-16 match in a Grand Slam tournament, took charge quickly. It was a reminder of the way he played at the start of the year, when he won 14 of his first 17 matches, all on hardcourts.
During that run, he reached the quarters of the Australian Open. Now he's back in another Grand Slam quarterfinal, again on hardcourts.