Naomi Osaka is over her first-night nerves as her bid to defend the US Open 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."

Wimbledon champion Simona Halep's disappointing record at Flushing Meadows continued with a defeat by Taylor Townsend.

The Romanian fourth seed made it past the first round for the first time in three years, but got no further after going down 2-6 6-3 7-6 (4) to the American qualifier.

Two-time Wimbledon winner 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."