Monte Carlo - American Taylor Fritz profited from Jo-Wilfried Tsonga's back problem, advancing 6-4, 2-0 on Tuesday when the Frenchman retired in the first round of the Monte Carlo Masters.
Tsonga's pullout after 57 minutes on court was a setback as he returns from 2018 knee surgery.
The Frenchman, who turns 34 on Wednesday, reached the semi-finals here in 2013 and 2016 but did not compete on the clay last spring.
He reached the semi-finals last week in Marrakech, losing to countryman Benoit Paire.
Fritz, ranked 65th, was making his Monte Carlo debut and ended a run of four first-round losses dating to February.
Results from the third day of the ATP Monte Carlo Masters on Tuesday (x denotes seeding):
Taylor Fritz (USA) bt Jo-Wilfried Tsonga (FRA) 6-4, 2-0 retired
Cameron Norrie (GBR) bt Adrian Mannarino (FRA) 6-4, 6-3
Pierre-Hugues Herbert (FRA) bt Fernando Verdasco (ESP) 6-4, 6-4
Felix Auger-Aliassime (CAN) bt Juan Ignacio Londero (ARG) 7-5, 7-6 (7/5)