Naomi Osaka sauntered into the second round of the China Open with a straight-sets victory over qualifier Zarina Diyas.

The US Open champion withdrew from the Wuhan Open last week due to illness, but eased to a 6-4 6-3 victory on her return in Beijing on Monday.

Osaka's serve was not firing on all cylinders, but the eighth seed broke five times to set up a second-round meeting with Danielle Collins.

The world number six from Japan said she had never been so tired in her life after losing to Karolina Pliskova in the Tokyo Open final in her homeland last month - missing out on back-to-back titles following her maiden grand slam triumph in New York.

Osaka appeared to have benefited from some rest as she unleashed powerful groundstrokes, wrapping up the opening set after claiming the first break to lead 5-4.

The 20-year-old breezed into a 5-1 lead in the second and although she was pegged back at 5-3 after failing to hold for a second time, Osaka went through by winning an entertaining rally after working the 91-ranked Diyas from side to side with rasping forehand and backhands.