Konta was beaten 4-6 6-3 6-4 by Serbia's Aleksandra Krunic, who goes on to face either Ajla Tomljanovic of Australia or Sweden's Johanna Larsson for a place in the last 32.

The 24-year-old grew in confidence after losing the opening set to outsmart the Wimbledon semi-finalist who was seen as a genuine contender for the title pre-tournament.

 

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Konta, 26, never looked comfortable against 78th-ranked Krunic and lost in two hours and 17 minutes.

Konta at least forced Krunic to serve it out but there were no nerves as she powered her way to three match points, taking the second when her opponent pulled a backhand well wide - her 42nd unforced error.

"I feel amazing, happy the way I played the way I fought," said Krunic during her on court post-match interview." I had to be at my best from the first point.

"Today it was all about intensity. I am proud of myself, I was tactically able to do the things I had in my head."

Heather Watson failed to end her miserable run of results at Flushing Meadows as she lost a seventh successive first-round match to Alize Cornet.

The British No 2 insisted ahead of the tournament that the sequence was simply coincidence rather than anything to do with the courts or the event.

Indeed, Watson won the junior tournament in 2009 but has not managed a single victory in the seniors.

This match was a frustrating one for the 25-year-old, who paid for poor starts in both sets and fell to a 6-4 6-4 defeat.

Wimbledon champion Garbine Muguruza notched up her first ever victory on Arthur Ashe Stadium with a 6-0 6-3 win over American Varvara Lepchenko.

Despite winning two Grand Slam titles, Muguruza has never felt at home at Flushing Meadows having never advanced past the third round.

"I have been here so many times and I've never done very well," said the Spaniard. "I give everything I have on the court.

"She started a little nervous and I started well. Then it got more equal and became a good fight."

Petra Kvitova, who returned to competition in May five months after being stabbed in her hand by an intruder at her home in the Czech Republic, scraped into the second round after beating former world No 1 Jelena Jankovic 7-5 7-5.

The Czech 13th seed, in search of top form after a mediocre build-up to the year's final Grand Slam, struggled to adapt to Jankovic's counter-punching style but eventually wore down the 2008 runner-up to set up a meeting with France's Cornet.

Ninth seed Venus Williams was given a scare by Slovakian qualifier Viktoria Kuzmova but recovered from losing the second set to win 6-3 3-6 6-2.

Greek hope Maria Sakkari upset 24th-ranked Kiki Bertens 6-3 6-4 while there were wins for Caroline Garcia, Magdalena Rybarikova and Kristyna Pliskova.