World number two Rafael Nadal's bid to win the Rome Masters for the fourth successive year was buried on Wednesday when he lost 7-5 6-1 to Juan Carlos Ferrero.
Ferrero, the 2001 champion, got the match-turning break at the end of tough first set.
The unseeded player then broke Nadal again in fourth game of the second and quickly finished off his Spanish compatriot, who had treatment on a foot injury at 4-1 down.
Nadal paid tribute to Ferrero but said the injury had hampered his performance.
"I have this pain in a point at the back of my foot, so it was tough for me," the 21-year-old told a news conference. "I just congratulate Juan Carlos. I think this is an important win for him because he's trying to go to the Olympics.
"I'm happy for him because he's a nice guy and a very good player."
Ferrero, a former world number one, was delighted at handing Nadal only his second defeat on clay in more than 100 matches.
"I had never won a set against him on clay so I'm pretty happy of course," he said.
"It's a very important win for me and I feel special right now. I haven't had this special feeling for a long time.
"I was so strong mentally today. I had things very clear in my mind."
Ferrero will meet Stanislas Wawrinka in the third round after the Swiss beat Britain's Andy Murray 6-2 7-6.
EARLY RESISTANCE
Russian fourth seed Nikolay Davydenko cruised in the third round with an 6-2 6-2 win over Croatian wildcard Mario Ancic, while Australian Open champion Novak Djokovic quelled some early resistance from Belgium's Steve Darcis to prevail 6-4 6-0.
Serbia's Djokovic had to recover an early break in the first set and save two break points in the ninth game before Darcis threw away his final service game of the set to love with a series of unforced errors.
The Belgian looked dismayed at having contributed to his downfall and the world number three was able to run away with second set to go through the third round.
Nadal was not the only top 10 seed to tumble. Argentine David Nalbandian, the seventh seed, lost an exciting match against Spain's Nicolas Almagro 6-4 7-5.
Nalbandian came off worse in a five-break first set and saved seven match points in two separate games before surrendering his serve at the end of the second.
Spanish fifth seed David Ferrer also suffered an upset, collapsing after taking the first set against Radek Stepanek of the Czech Republic to go down 4-6 6-2 6-1.
However, American James Blake, the eighth seed, laboured to a 7-6 3-6 6-1 win over Italy's Andreas Seppi.
Roger Federer moved into the third round on Tuesday with a 6-3 6-3 victory over Guillermo Canas. The world number one will face Croatia's Ivo Karlovic, who beat Italy's Potito Starace 6-3 6-7 7-6.
(Editing by Clare Lovell)