Nicolas Mahut of France upset third-seeded Andreas Seppi of Italy 6-4, 6-4 to reach the Moselle Open quarterfinals on Thursday.
Mahut broke last year's runner-up twice in each set. The Frenchman won two titles in the summer and is enjoying his best season.
Florian Mayer and Benjamin Becker of Germany also advanced to the last eight.
The eighth-seeded Mayer did not face a break point in his 6-3, 6-2 victory over Lukas Lacko of Slovakia, while Becker outlasted French wild card Albano Olivetti 6-7 (8), 6-3, 6-1.
Olivetti rallied from 6-2 down in the tiebreaker to win the first set.
But Becker broke Olivetti twice in the next set to even the match. The German took leads of 3-0 and 5-1 in the third set.