Russia's Igor Andreev defeated Andre Agassi in three sets to book a place in the third round of the Stella Artois Championship at Queen's Club.
The unseeded 20-year-old came back from a set down to win 4-6 7-6 (7-2) 7-6 (7-3) against his boyhood hero.
"I can't believe it. It's amazing, it's like a dream for me to beat Andre Agassi. He's my idol," said Andreev.
Agassi, 34, won the first set easily but could not compete with his opponent in the two tiebreaks.
The American later failed to attend a press conference and could face a $1,000 fine for his no-show.
It was the first time since 1997 he has lost his opening match of a event three times in succession, following on from shock defeats at St Polten and the French Open.
The former Wimbledon champion, who has won all four grand slams at least once, has only won two matches since March and is stuck on 799 career wins.
But his doubles partner at Queen's, Andy Roddick, was unconcerned.
"It happens with all players. He's not hitting the ball as
well as he wants to in the matches. We've been practising and
he's been practising great," he said.
" And we played doubles yesterday and he was hitting the
ball perfect. If there's one thing I know, it's not to worry
about Andre Agassi."