Nara claimed a 7-5, 7-6 (7-4) decision over eighth-seeded Monica Puig in a match that took nearly 2 hours. Nara won the first set with her second of two breaks and had another break in the second that led to the tiebreaker.
She won 62 percent of the points on serve but took just four more (83-79) points overall. Nara was born in Osaka and lives in nearby Hyogo.
Third-seeded Samantha Stosur and No. 5-seeded Eugenie Bouchard both had solid wins in gaining spots in the quarterfinals. Stosur dispatched Belinda Bencic 6-4, 6-2 by going 5-for-5 in break opportunities while Bouchard beat Luksika Kumkhum 6-2, 6-2 behind six breaks.