Carlos Alcaraz has been knocked out of the Monte Carlo Masters in only the second round after losing 7-6(2) 6-7(5) 6-3 to Sebastian Korda.
The world No. 11 was expected to make a deep run in the Masters competition having won the Miami Open last month.
But the Spaniard was unable to cope with the American - who he beat in the 2021 ATP Next Gen final last year - on Court Rainier III in a match which lasted three hours and one minute.
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Korda is the first player outside the top 10 to beat Alcaraz since November. Alcaraz's win-loss record is now 18-3 in 2022 and 6-1 on clay.
Korda will play reigning Indian Wells champion Taylor Fritz in the next round after he beat 2014 US Open champion Marin Cilic 6-3 4-6 6-4.
“It was nice to get the victory today," Korda, who is making his Monte Carlo debut, said after the match.
"I stayed calm and believed in my returning. It was super tough, every time he threw up the ball it moved around. It was a crazy match."
Korda raced into a 4-2 lead in blustery conditions in the opening set before Alcaraz fought back with three straight games of his own.
Alcaraz twice failed to serve out the set and Korda forced a tie-break which the 21-year-old took the lead in.
Korda, whose only tour level title was won on clay at an ATP 250 event in Parma last year, had to fight back from 3-0 down in the opening stages of the second set and also saved three set points on serve at 4-5 before holding on to force a tie-break.
This time the tie-break would go Alcaraz's way as he began to play with greater consistency and variety.
Both players attempted to drag each other around the court in the decider and it was Korda who sealed the pivotal break to move into a 5-3 lead before serving out the set to secure a shock victory.
Reflecting on the defeat, Alcaraz said: "I’m a bit disappointed with myself. I had a lot of chances to be up in the match and close to winning, but these losses sometimes [are] good to live.
"I didn't think about the expectations that the people have [for] me. I just focussed on me and what I have to do. But as I said, you have to play more matches on clay courts."
Alcaraz is set to compete at the Barcelona Open ATP 500 tournament next week.
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