Rafael Nadal's bid for a 12th Monte Carlo Masters title was shattered by Russia's Andrey Rublev, who swept to a 6-2, 4-6, 6-2 quarter-final win on Friday with the great Spaniard admitting his serve was "a disaster".
Nadal, bidding to reach the semi-finals of a Masters for the 75th time, followed world number one Novak Djokovic, who was beaten in the third round, out of the tournament.
"Today was one of those days that my serve was a disaster," said world number three Nadal.
"It's always sad to lose here. I missed an opportunity to start the clay court season in the right way. But that's it. It's not the moment to complain.
"The only thing that I can do is go to Barcelona (where he plays next week) and keep practicing, try to fix the things that didn't work well."
Despite Friday's setback, 34-year-old Nadal will still be favourite to capture a 13th Roland Garros title in June and record-setting 21st major.
"For Rafa, it must be incredibly difficult to play with this pressure of always having to win," said Rublev who also made the Miami Masters semi-finals at the start of April.
"I'm shocked to see the level which he can reach despite this pressure. It's much easier to play when you have nothing to lose."
It was only the second time in 16 appearances in Monte Carlo that Nadal had failed to make the semi-finals.
World number eight Rublev will face unseeded Casper Ruud, who put out defending champion Fabio Fognini, for a place in the final.
The other semi-final will feature Greek fourth seed Stefanos Tsitsipas against Britain's Dan Evans, the man who shocked Djokovic.
Tsitsipas is now the highest seed left after world number two Daniil Medvedev was forced to withdraw due to a positive Covid-19 test.
Rublev is no stranger to taking out the big names -- back in 2019, he stunned Roger Federer at Cincinnati in just 62 minutes.
On Friday, the 23-year-old won the first set in 38 minutes but Nadal then pocketed the last four games of the 73-minute second set to level the contest.
- Rublev 'deserved it' -
In the decider, Rublev held his nerve, breaking the Spaniard three times on his way to a famous win, his first in three meetings with Nadal.
"He played well, he deserved it more than me," added Nadal.
"But you can't expect win against a player like him losing my serve I don't know how many times -- six, seven times? It's too much."
Tsitsipas advanced to the last-four when Alejandro Davidovich withdrew after losing the first set 7-5.
Tsitsipas, the world number five, will play his sixth Masters semi-final, and his first in the principality, against Evans, who battled past Belgian David Goffin 5-7, 6-3, 6-4.
Struggling with an injury to his left thigh, Spaniard Davidovich tried an underarm serve when facing set point.
Tsitsipas pounced to hit a winning backhand return with his opponent quitting after dropping the opener 7-5.
"I noticed he was hurt. His leg was hurting. But I didn't want to think about it, I tried to pretend he wasn't injured and keep playing as I was doing," said Tsitsipas.
Evans edged Goffin after the Belgian made 47 unforced errors, including a final forehand on match point, to win.
"I played good today. I felt a bit more pressure to not just win yesterday and give a bad performance today," said Evans, 30.
Unseeded Ruud won 6-4, 6-3 against 15th seeded Fognini, making the last four in Monte Carlo 24 years after his father Christian had reached the quarter-finals.
Rublev holds a 3-0 record against Ruud, which includes back-to-back clay-court wins at Hamburg in 2019 and 2020.
"I've gained good confidence from this week and I've beaten good players," Ruud said.
"I have to try to find a way to believe that I can win."