Tennis news - Osaka stays calm to see off Linette

After struggling with nerves in her gruelling first-round match, Osaka was calm and collected on Louis Armstrong Stadium court, smacking 13 winners and playing stout defence to dispatch Poland's Linette.

After a one-sided first set, trouble brewed for the world number one when Linette raced out to a 3-0 lead in the second on a sun-soaked court.

But the 21-year-old Japanese kept her composure and battled back, hitting a deft volley on match point to seal the win before an adoring crowd including former San Francisco 49er Colin Kaepernick and former Los Angeles Laker Kobe Bryant.

Next up for Osaka is either qualifier Timea Babos or 15-year-old American wildcard Coco Gauff.

Elsewhere, Andrea Petkovic upset sixth seed Petra Kvitova 6-4, 6-4 to set up a third-round clash with Elise Mertens.

World number 88 Petkovic was the better player in the biggest points, breaking the twice Grand Slam champion three times and committing 15 fewer unforced errors on a sun-soaked Louis Armstrong Stadium court.

The 31-year-old German, who celebrated the win by lifting her shirt and pointing to her abs, said she is in a great state of mind despite winning only eight main-draw matches this year.

"In the past two weeks I've been really good with my mental state," Petkovic said.

"I've been trying to stay in the moment and play point by point, enjoy the time I get to spend on this beautiful court and it's been really working for me, so I'm glad.

"There were ups and downs throughout the match but I was there in the most important moments."

25th seed Mertens trounced Kristyna Pliskova 6-2 6-2.