Rotterdam - Top-seeded Juan Martin del Potro has beaten France's Paul-Henri Mathieu 6-2, 7-6 (2) to book his berth in the quarter-finals of the ABN Amro tournament in Rotterdam.
The Argentine, who is recovering from a wrist injury, breezed through the first set before the pace slowed considerably in the second.
Del Potro, last year's winner, survived two break points and both players held serve until the tiebreaker.
Earlier Thursday, third seed Czech Tomas Berdych beat Nicolas Mahut 6-4, 6-3, while fifth seed Jo-Wilfried Tsonga crashed out against Marin Cilic 4-6, 4-6.
Later, second seed Andy Murray is to play Dominic Thiem.
Results from the fourth day of the $1.3 million ATP World Tennis Tournament in Rotterdam on Thursday (x denotes seeding):
Juan Martn Del Potro (ARG x1) bt Paul-Henri Mathieu (FRA) 6-2, 7-6 (7/2)
Tomas Berdych (CZE x3) bt Nicolas Mahut (FRA) 6-4, 6-3
Jerzy Janowicz (POL) bt Tommy Haas (GER x6) 6-4, 6-4
Ernests Gulbis (LAT) bt Grigor Dimitrov (BUL x8) 6-4, 7-6 (7/3)
Philipp Kohlschreiber (GER) bt Richard Gasquet (FRA x4) 7-5, 7-5