Top-seeded Janko Tipsarevic of Serbia was made to work for victory against Austrian qualifier Martin Fischer at the Swiss Open before sealing a 4-6, 7-6 (1), 6-3 second-round win on Thursday.
Tipsarevic is seeking back-to-back clay-court titles after winning the tournament in Stuttgart, Germany, last week.
Two other seeds in action both lost, leaving Tipsarevic and No. 5 Feliciano Lopez as the only seeded players in Friday's quarterfinals.
Defending champion Marcel Granollers, the No. 2 seed from Spain, lost 6-4, 6-2 against Lukasz Kubot of Poland.
Czech qualifier Jan Hernych, who played through three rounds to reach the main draw, beat seventh-seeded Santiago Giraldo of Colombia 6-3, 2-6, 6-4.
Grigor Dimitrov of Bulgaria beat Dustin Brown of Germany 7-6 (3), 3-6, 6-2.
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