Kei Nishikori beat Pablo Andujar, 6-3, 6-3, on Wednesday in the ATP Tour's Rogers Cup in Montreal.
The fourth-seeded Nishikori, a finalist last year in the U.S. Open, earned his tour-leading 27th hard-court win of the season in the second-round match that was delayed nearly 90 minutes by rain.
David Goffin, seeded 13th, will be Nishikori's opponent in the round of 16 on Thursday. Goffin beat Sam Querrey, 6-4, 6-4.
Seventh-seeded Rafael Nadal got his tournament started with a 7-6 (4), 6-3 victory over Sergiy Stakhovsky.
Nadal will face Mikhail Youzny, a 6-1, 6-4 winner over ninth-seeded Gilles Simon.
Second-seeded Andy Murray beat Tommy Robredo, 6-4, 7-5 in a rain-delayed match that started Tuesday night.
American Jack Sock downed 14th-seeded Grigor Dimitrov, 5-7, 7-6 (5), 7-5 to advance to a meeting with top-seeded Novak Djokovic.
Defending champion Jo-Wilfried Tsonga, seeded 10th, outlasted Roberto Bautista Agut, 5-7, 7-6 (6), 7-5.
In Toronto, Ukrainian qualifier Lesia Tsurenko upset Garbine Muguruza, 7-5, 6-1, in the Rogers Cup.