Simona Halep's advice to Taylor Townsend came back to bite her after the American qualifier dumped the Wimbledon champion out of the US Open.

Townsend, ranked 116 in the world, came from behind to stun the Romanian fourth seed in a third-set tie-break, winning 2-6 6-3 7-6 (4).

Halep beat Townsend 6-1 6-3 at the Miami Open in March, after which the 23-year-old asked for some tips.

Halep revealed: "After we played together, she came in the locker room and she asked me what she has to improve to be better. Next time I will not say anything."

Townsend, who will face Sorana Cîrstea in round three, recalled: "I don't know why I did it, but I did it. It kind of stuck with me.

"I'm not saying that everything she said I implemented into my training, but it was definitely in the back of my head to remember what she said and also remember why I asked, what drove me to ask that question, kind of that hunger and desire to get better."

Naomi Osaka is over her first-night nerves as her bid to defend her title gathers pace.

Osaka needed three sets to dispatch Anna Blinkova in her first-round match, but there was no such drama in her 6-2 6-4 win over Magda Linette.

"For me, going into this match I was very calm, because I was thinking there is no way my nerves could be worse than they were the day before," she said.

"For me, I also had that comfort of knowing I have played Magda before. I'd never played Blinkova before, so there is also that added stress not knowing what she can do.

"For me, that stress was taken away today. I came in pretty confident with my abilities and I think that showed a little bit."

Two-time Wimbledon champion Petra Kvitova was another surprise second-round casualty, the sixth seed losing 6-4 6-4 to Andrea Petkovic.

"I think that she likes my game, to be honest," said the Czech. "She played great. She moved pretty well as well.

"I had my chances, but I was always missing the last things. I was a break up in the second, and I should make it.

"But, yeah, overall I don't think I really played that bad. That's how it is. I was really trying hard. I was fighting."

Teenage wild card Coco Gauff is through after a 6-2 4-6 6-4 win over Hungarian qualifier Timea Babos.