Qualifier Martin Klizan produced a fine attacking display to shock Novak Djokovic 6-2 1-6 6-3 and reach the third round of the Barcelona Open on Wednesday.
The defeat is a blow to Djokovic as he continues his recovery from elbow surgery and he must now reassess his schedule ahead of next month's French Open.
The injury coincided with a prolonged slump in form for the 12-time major champion, although a reunion with long-time coach Marian Vajda earlier this month had sparked hopes Djokovic could return to his best.
But despite encouraging signs in Monte Carlo last week, and Djokovic declaring there he was finally playing without pain, he was well below his best against world No 140 Klizan, who was rewarded for aggressive and enterprising tennis.
"I feel I haven't lived up to your expectations, not even my own," said Djokovic. "Its hard to deal with these types of games and defeats, I wasn't playing at my best, only during the second set. I will try to continue and see where it takes me."
The first set, powered by his powerful left-handed forehand, brought two breaks of serve, before Djokovic found some much-needed rhythm to race through the second.
But with the advantage of serving first in the deciding set, Klizan kept his cool to restore his authority and keep his nose ahead.
The set went with serve until a hesitant Djokovic volley with the court at his mercy then allowed Klizan to fire a backhand down the line, to which the former world No 1 had no answer, and force the break at 5-3.
And having littered the first set with drop shots, the 28-year-old pulled out an exquisite example to earn three match points.
The first slipped by with a nervous double fault, but he won it on the second as Djokovic pounded a forehand from well behind the baseline into the net to seal Klizan a third-round clash with Feliciano Lopez.
"It was a good match," said Klizan. "I know Novak is coming back from a tough time and injury, I know how hard it is. I want to wish him all the best. I'm sure he will come back stronger.
"I always play good tennis in Barcelona. This was the first time I played him on clay and I beat him and it feels great. I know he didn't play top tennis but a win is a win."
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