Defending champion Rafael Nadal suffered a shock 6-4 6-2 defeat by Italian Fabio Fognini in the semi-finals of the Monte Carlo Masters.
The 32-year-old Spaniard, seeking his 12th Monte Carlo title, had won his past 18 matches at the event and lost only four of 75 in his career.
World number 18 Fognini will face Serb Dusan Lajovic in Sunday’s final.
“I played one of my worst matches on clay in 14 years,” said world number two Nadal.
“It’s difficult to find any positives. I deserved to lose.”
World number 48 Lajovic reached his first ATP final with a 7-5 6-1 win over Novak Djokovic’s conqueror Daniil Medvedev.
Lajovic, 28, came from 5-1 down to win 10 successive games against the 10th seed and become the lowest ranked Monte Carlo finalist since 2001.
Fognini, who was a set and 4-1 down to Andrey Rublev in the first round, won in one hour 36 minutes to reach a Masters 1000 final for the first time.
He became only the fourth player to win three or more matches against Nadal on clay, and the first Italian to reach the Monte Carlo final since Corrado Barazzutti in 1977.
Playing his first tournament for a month after opting to rest his troublesome knees, Nadal added: “I had a bad feeling; it was a tough day.
“I’m coming from low moments in terms of injuries, and in terms of the mental side it has not been easy to accept all the things that have been going on during recent weeks.
“Everything was wrong. I always expect the best. But you have to be ready to accept the negative things, and it was a negative day.”
Britain’s Jamie Murray and Brazilian partner Bruno Soares lost 7-6 (7-4) 6-4 to Dutchmen Robin Haase and Wesley Koolhof in the doubles semi-finals.