Nishikori in four
Sixth-seeded Kei Nishikori of Japan, two years removed from his run to the final, rallied for a 4-6, 6-1, 6-2, 6-2 win over France's Nicolas Mahut.
Nishikori, who has dropped a set in each of his matches so far, next faces big-serving Croatian Ivo Karlovic, a 6-4, 7-6 (7/3), 6-3 winner over US qualifier Jared Donaldson.