Top seed Andre Agassi suffered a shock defeat in the first round of the St Poelten Grand Prix in Austria on Monday, losing 6-2, 7-6 to Serbian journeyman Nenad Zimonjic.

"Nobody is more surprised than I am," Agassi told reporters after his one hour 26 minute humiliation against a player better known as a doubles specialist.

"I did not move well, I was only reacting," added the world number six.

Zimonjic, ranked 339 in the world, was leading by a set and 4-1 before Agassi finally woke up.

The 34-year-old American, winner of all four Grand Slam titles during his illustrious career, went ahead 5-4 only to falter again and lose the match on a tiebreak.

"This is a dream come true for me," Zimonjic said.

Agassi, who had not played a competitive match since March, was hoping to gain some valuable claycourt practice for the French Open later this month -- a tournament he won in 1999.