"It's in Mexico at 1,500 metres and they're using pressureless balls," said Craig Tyzzer, coach to the world No. 1.

The American trailed the No. 1 by 2-5 in the third set—and took off from there.

The Australian hit 11 of them during her first-round win over Vera Zvonareva on Tuesday.

Meanwhile, No. 1-ranked Ashleigh Barty opens her campaign against a former No. 2.

Could the Grand Slam season end with a showdown between world No. 1 Ash Barty and defending champion Naomi Osaka? It won’t be easy; there are a lot of hoops to jump through.

The world No.1 picked up her fifth title of the season at the Western & Southern Open.

The Aussie looks in dominant form after winning Cincinnati's Western & Southern Open for the first time.

She improved to 40-7 on the year on Sunday with a 6-3, 6-1 win over Jil Teichmann in the final of Cincinnati.

The WTA world No. 1 improved to 6-0 in semifinals this season with a 6-2, 7-5 victory over the lefty at the Western & Southern Open Saturday.

The world No. 1 reeled off the final four games of an entertaining Western & Southern Open quarterfinal clash.