The Swiss progressed 6-1 7-5 to set up a last-eight meeting with Dmitry Tursunov, who beat Pablo Carreno Busta 6-2 6-4.
Fourth seed Jurgen Melzer overcame qualifier Mischa Zverev 7-5 6-4 despite failing to find his best form.
"It's always difficult, and I was struggling today [Thursday]," Melzer said.
"I didn't play my best tennis, but at the end of the day it's just important that you have a next match to play.
"I think in general I'm hitting the ball well and I just have to find my rhythm in the tournament. Once I have that I think I can go really far, but first I have to get there.
"So the next round is my next chance to get that rhythm."
Joao Sousa fought back after losing the first set to Pablo Cuevas 4-6 7-5 6-0 while Frenchman Julian Benneteau was a 7-6 (10/8) 6-2 winner against Pablo Andujar.