British number one Kyle Edmund let an early lead slip as he was beaten in the first round of the Monte Carlo Masters by Diego Schwartzman.
World number 23 Edmund led Argentina's Schwartzman by a set and 3-0 but ultimately lost 4-6 6-3 6-1.
The 24-year-old won only one of the final 13 games against Schwartzman, who is one place below him in the world rankings.
Schwartzman will face either Jo-Wilfried Tsonga or Taylor Fritz next.
There were five breaks of serve in a scrappy opening set before Edmund converted his first set point.
The Briton broke Schwartzman at the first opportunity in the second set but Schwartzman won nine straight games to level the match and take an early third-set lead.