Making the most of fast starts to both sets, Zhang completed a 6-3, 6-2 win in style, firing a wonderful forehand winner into the corner.
This year Osaka has started to deliver on her boundless potential, but against Zhang was unable to find the consistency to match her shotmaking. She netted a forehand to fall an early break behind and despite reducing her arrears to 4-3 was unable to rescue the first set.
Zhang continued to play the steadier tennis in the second set, punctuating her metronomic groundstrokes with occasional moment of inspiration; with Osaka serving at break point down in the second game, Zhang soaked up a series of heavy-duty groundstrokes before arrowing a pin-point forehand onto the baseline.
Another break soon followed as she confidently set up a quarterfinal meeting against Varvara Lepchenko.
To the delight of the crowd Kurumi Nara produced one of her best performances of the year to swat aside No.3 seed Putintseva and keep live homes of a Japanese champion. McHale, the No.7 seed, was made to work considerably harder, coming within two points of defeat against qualifier Rebecca Peterson before pulling through, 2-6, 6-2, 7-6(4).
"It was a very tough match, very physical - the points were very long - so I'm really happy to have won and be moving on to the next round," McHale said.
Fellow American Alison Riske continued her impressive progress through the draw, easing past Misaki Doi's conqueror, Aliaksandra Sasnovich, 6-3, 6-1, while Viktorija Golubic defeated last year's finalist Magda Linette, 6-2, 6-7(5), 6-3.