The Spaniard was beaten, 7-6 (7), 6-2, by eighth-seeded Stan Wawrinka in the Italian Open quarterfinals Friday; his fifth loss on clay this season.
Nadal wasted four set points in the tiebreaker, surrendering a 6-2 lead.
"I didn't have enough leg in some moments today. He played crazy. He hit amazing shots in a lot of moments, and especially important ones," Nadal said. "At 6-2 he played a lot of good points.
"I am not very happy with the way I played," Nadal added. "During the night the ball is bigger, the bounces are not that high. So he has the chance to go for it. And he was on fire."
The last time Nadal was beaten so many times on his favorite surface was 12 years ago — in his rookie season.
Nadal has won the French Open nine of the past 10 years. But he's struggling to get back to his best after a wrist injury and an appendectomy last season.
On Monday, Nadal dropped out of the top five in the ATP rankings for the first time in 10 years — falling to No. 7. That will give him a tough draw in Paris, where play starts next weekend.
"I am ready to accept the challenge," Nadal said. "If I go to Roland Garros (and) I lose (and) I don't play well, life continues. It's not the end of the world. I won so many times there. I don't want to (win) 15 Roland Garros. That's for sure. It's normal that I can lose. Losing is part of life."
But, he added: "I am sure that I can be competitive."
Nadal had won all 12 of his meetings with Wawrinka until the Swiss player beat him in last year's
"I was looking for some win to get my confidence back and this is a perfect match for that," Wawrinka said. "To beat Rafa on clay is something amazing for me."
Wawrinka raised his arms in triumph to celebrate and sent a message to his semifinal opponent — fellow Swiss player
Federer kept up his pursuit of an elusive title with a 6-3, 6-3 win over sixth-seeded
Rome and Monte Carlo are the only Masters series titles that the 17-time Grand Slam champion has never won.
Top-ranked Novak Djokovic, meanwhile, was pushed to three sets for the third consecutive match in a 6-3, 3-6, 6-1 win over fifth-seeded
Djokovic's semifinal opponent will be seventh-seeded
In the women's tournament, two-time Rome champion
Sharapova will face Daria Gavrilova of Russia, who beat
Djokovic, the defending champion also went three sets against
"(There were) ups and downs for my side in all three matches," Djokovic said. "This is what it takes to win, just finding the proper way and managing to perform your best when it matters."
Federer fell behind a break midway through the first set but recovered immediately and cruised from there.
"From the baseline I was playing very well." Federer said. "My serve was not quite there from the beginning. I was hitting too many second serves and he was able to take advantage of that and break early. So it was important to pick it up on the serve, which is maybe the easiest thing to do."
"I felt good again on the return and (was) moving well, so as the match went on I got better and better," he added. "The wind picked up in the second set — that's when I think Tomas didn't play so well anymore and I was able to get the job done."
After winning a title on clay in Istanbul two weeks ago, Federer lost his opening match to Australian Nick Kyrgios at last week's Madrid Open. But he has played solidly here, also beating