A year after winning her maiden Grand Slam title at the U.S. Open, Svetlana Kuznetsova suffered the humiliation of becoming the first defending women's champion to lose in the opening round on Monday.
By contrast, fellow Russian Maria Sharapova and men's second seed Rafael Nadal started their campaigns in irresistible style.
An out-of-sorts Kuznetsova stomped off court stony-faced after being thrashed 6-3, 6-2 by little-known compatriot Ekaterina Bychkova.
Sharapova, the women's top seed, demolished Greece's Eleni Daniilidou 6-1, 6-1 with a pugnacious display of hitting on Arthur Ashe Court. Spanish teenager Nadal beat American wild card Bobby Reynolds 6-3, 6-3, 6-4.
Argentine ninth seed Gaston Gaudio suffered a premature exit, losing 7-6, 6-2, 6-4 to U.S. wild card Brian Baker but Andre Agassi and women's contenders Kim Clijsters and the Williams sisters, Serena and Venus, recorded impressive first round victories.
Fifth seed Kuznetsova has struggled to live up to her success last year, failing to win a single title in 2005 and the 20-year-old looked burned out on Louis Armstrong Court.
Bychkova, also 20 but ranked only 97 and making her grand slam debut, dominated from the start while Kuznetsova ballooned errors from all angles.
"Of course I'm disappointed," Kuznetsova said. "But things like this happen. I just didn't play my game. I will learn from it. I just want to have some time off."
Her defeat gave Russia a disappointing Grand Slam double in 2005. Anastasia Myskina also lost as defending champion in the first round of this year's French Open.
Sharapova has never been beyond round three at Flushing Meadows but was clinical in her disposal of Daniilidou, who upset Belgian Justine Henin-Hardenne in the Wimbledon first round in June.
The 18-year-old Russian, resplendent in a sky blue dress with yellow trim, has been suffering with a pectoral injury but she said: "It felt really good. I feel a lot stronger in my arm. I moved quite well today. I don't think I moved that well in quite a while."
Reigning French Open champion Nadal, the 19-year-old Spaniard who has won nine titles this year and risen to number two in the world, displayed flashes of his usual panache in beating American wild card Bobby Reynolds 6-3, 6-3, 6-4.
"The first match is never easy," the teenager said. "I didn't play very, very well today, but the most important thing is to win the match."
Gaudio, the 2004 French Open champion, offered little resistance after losing the first set tiebreak 11-9 to Baker, who took advantage to record his first victory at a grand slam event and only the fourth win of his career.
Seventh seed Agassi, now 35 and embarking on his 20th U.S. Open campaign, recorded a sprightly 6-3, 6-3, 6-1 win in the final night session match in only 69 minutes against Romania's Razvan Sabau.
"I was pretty nervous coming out here today," said the Las Vegan, who has a troublesome back complaint.
"It took me a while to settle in. But it felt good."
Women's eighth seed Serena showed little sign of her nagging knee and ankle injury when she overwhelmed Taiwanese 16-year-old Yung-Jan Chan 6-1, 6-3. Fourth seed Clijsters made even shorter work of German qualifier Martina Mueller, winning 6-1, 6-2.
Serena trailed 3-1 in the second set after losing her serve before reeling off the next five games.
"I was playing really flat and lazy (in the second set) so I said, 'Ok, Serena let's pick it up and play.' I feel awesome. I feel I have no pressure," the Australian Open champion said.
Older sister Venus, the Wimbledon champion and Serena's potential fourth round opponent, mirrored her sibling's winning scoreline by outclassing Japan's Rika Fujiwara 6-3, 6-1.
"I feel like I'm playing better than Wimbledon," Venus said.
Against Mueller, Clijsters showed the form that has brought her six titles this year, although she is still seeking a first grand slam title.
The hard-hitting Belgian needed only 53 minutes to complete an impressive workout on the Louis Armstrong court, sealing her victory with a thunderous first serve.
"It feels great," Clijsters said. "I'm very happy with the way I've been playing the whole summer here in America."
Australian 14th seed Alicia Molik, whose year has been badly disrupted by an inner ear infection, was knocked out 6-4 6-4 by Shenay Perry of the United States.