Carlos Alcaraz slumped to a third round defeat at the Italian Open to unheralded Hungarian Fabian Marozsan on Monday, just two weeks before he heads into the French Open as top seed.
The 20-year-old Spaniard, who is guaranteed to replace Novak Djokovic as world number one on May 22, had come into the tournament in Rome on the back of wins in Barcelona and Madrid.
But the US Open champion was outplayed by 23-year-old Marozsan, losing 6-3, 7-6 (7/4).
Marozsan, who is ranked 135th in the world, won the final six points of the second-set tiebreaker to give Alcaraz a wake-up call with the French Open starting in less than a fortnight.
Alcaraz, who was second seed in Rome but in Paris will be top seed at a Grand Slam for the first time, said he required some sustained training to beef up his French Open preparations with the clay court major beginning on May 28.
"I'm going to rest a little bit, some days off for me," he said. "I really need some days to reset my mind and be fresh for Roland Garros.
"If I want to go to Paris in good shape, I have to practise, to be better. I've been playing so much that I couldn't practise more than three, four days in a row.It's going to be really helpful for me to have days at home practising and getting ready to go to Roland Garros."
He admitted he was outplayed by his Hungarian opponent.
"He surprised me a lot, his level was really, really high. I'm sure he's going to break the top 100 very, very soon."
Marozsan, who next plays Borna Coric for a place in the quarter-finals, had not won a match on the ATP Tour prior to the tournament -- indeed this is the first time he has qualified for the main draw at a tournament on the Tour.
"Everything was perfect today, I was doing my job," the winner said. "I cannot imagine this win, even if it was my dream last night.
"I thought I might win a few games or a set."
Marozsan produced 24 winners in a victory which took an hour and three quarters.
"I had hoped I could do something special," he said. "Now I've just beaten the best in the sport so I'm very happy."
Alcaraz now stands 30-3 for the season.
In other results at the ATP-WTA tournament, sixth seed Andrey Rublev defeated Spain's Alejandro Davidovich Fokina 7-6 (10/8), 6-3.