Huesler was serving at 5-6 in the deciding set to force what seemed to be an inevitable final-set tie-break. But in the first point of the game, the 25-year-old hurt a toe on his left foot and was unable to continue. Lopez therefore advanced to the second round 6-4, 4-6, 6-5 15/0.
The 39-year-old won his only ATP Tour clay-court title in Gstaad in 2016, and he was also a finalist here in 2006. Lopez is now 23-11 at the ATP 250, and he will next play Swede Mikael Ymer, who eliminated French lucky loser Enzo Couacaud 4-6, 6-3, 6-3 in one hour and 53 minutes.
This will be the first ATP Head2Head meeting between Lopez and Ymer. However, the Spanish lefty beat Ymer’s brother, Elias Ymer, in the Gstaad quarter-finals five years ago.
In other action, sixth seed Benoit Paire ousted Slovakian Jozef Kovalik 6-3, 7-6(2). The Frenchman, who made the Hamburg quarter-finals last week, hit a shot of the year contender, carving an incredible backhand drop volley with so much backspin, it bounced back to his side of the net.
Belgian 22-year-old Zizou Bergs continued his impressive year with a 7-6(3), 6-1 victory against fellow qualifier Oscar Otte of Germany. Bergs has won three ATP Challenger Tour titles this year and is at a career-high No. 212 in the FedEx ATP Rankings.
Czech qualifier Vit Kopriva and Australian Marc Polmans also advanced on the first day of main draw action, with both men defeating Swiss players. But the home favourites earned a doubles triumph when Jakub Paul and Leandro Riedi defeated Americans Evan King and Max Schnur 6-3, 6-4.