The world number six from Japan broke Diyas in the ninth game before claiming the opening set and she reeled off four games in a row before closing out victory.
Australian Open champion Caroline Wozniacki beat Switzerland's Belinda Bencic 6-2 6-3 while former world number one Garbine Muguruza of Spain dispatched Russian Ekaterina Makarova 6-0 6-4.
American Madison Keys pulled out with a knee injury before her match against Anastasija Sevastova, local hope Zhang Shuai upset 15th seed Elise Mertens 6-1 3-6 6-3 and seventh seed Karolina Pliskova cruised past Australian Samantha Stosur 6-4 6-4.
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(Reporting by Manas Mishra in Bengaluru, editing by Ed Osmond)
