Andre Agassi's run of 11 straight wins came to a surprise end when he was beaten 6-4 7-5 by qualifier Nicolas Thomann of France in the first round of the Atlanta Challenge.
Agassi, coming off title triumphs in the Tennis Masters Series events at Indian Wells and Miami, was outplayed in his first match of the year on clay by an opponent who was gaining his maiden win at ATP level in 2001.
Two other seeds fell in second round action.
Hyung-Taik Lee of South Korea beat third-seeded American Michael Chang 6-4 7-6 (7-3) in a night match. Earlier, Xavier Malisse of Belgium crushed fourth seed Rainer Schuettler of Germany 6-1 6-1.
Top seed Agassi, broken in the first game after opening up with three double faults, failed to threaten Thomann's serve in the first set.
But Thomann, who has only played Challenger tournaments so far this year, had to survive two set points while serving at 6-4 4-5 in the second.
"It's fabulous," said Thomann who has never been in the world's top 100. "It was a dream to play against a player so great.
"The first point, I entered the court to win the match, even if it was Agassi. You don't know what happens."
Agassi brushed off suggestions he could win the Grand Slam this year.
"The Grand Slam is nonsense," said the Australian Open champion. "I've got to start executing my game and I've got to find a way to get through these matches."
Meanwhile Chang, off to the worst start to a season of his career, saw his 2001 match record fall to 3-8 as Lee picked up his first victory outside Davis Cup play.