New York, United States, 28 August 2013 | AAP

Sam Stosur has crashed out of the US Open with a shock three-set first-round loss to American qualifier Victoria Duval.

The 2011 champion gave up a one-set lead to lose 5-7 6-4 6-4 to the 17-year-old world No.296 at Flushing Meadows on Tuesday.

Stosur appeared on track for a second-round meeting with veteran Slovak Daniela Hantuchova when she led by a set and 4-2, but collapsed to one of her worst defeats.

Stosur was undone by 56 unforced errors and 10 double faults and rued not ramming home her second-set advantage.

“By far I didn’t do enough from 3-love up, 4-2 up in the second,” she said.

“Yeah, I just let every single opportunity slip away, made way too many errors. At the end of the day, it really cost me.”

Teenager Ash Barty is the lone Australian left in the women’s singles draw after first-round losses earlier on Tuesday for qualifiers Olivia Rogowska and Casey Dellacqua.

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Playing her first match since splitting with long-time coach David Taylor just 11 days ago, Stosur made a confident enough start, grabbing an early break and racing to a 3-0 lead.

But the 11th seed developed the wobbles as Duval, a much better player than her world ranking reflects, raised her game on the Louis Armstrong Stadium show court.

Stosur dropped serve for the first time in the fifth game, double-faulted to gift Duval another break point in the ninth game and framed a forehand into the crowd to fall behind 5-4.

But Duval stumbled trying to serve out the opening set, double-faulting herself and Stosur took full advantage to get back on level terms.

Stosur held serve for 6-5 and closed out the opening set with a booming off-forehand winner.

The job wasn’t finished, though, as Stosur blew a 4-2 lead in the second set to enable the plucky young American to force a decider.

Stosur saved three match points before eventually succumbing, holding several break points in the final game which, if converted, would have seen her level scores at 5-5.

Stosur had arrived in New York full of confidence after winning nine of her 11 matches on American hardcourts over the US summer.

She ended her two-year title drought since beating Serena Williams in the 2011 US Open final with a breakthrough victory over world No.2 Victoria Azarenka at the Southern California Open three weeks ago.

Now the 28-year-old is poised to slip further down the rankings from No.11 after failing to defend her run to the quarterfinals at Flushing Meadows last year.

Her premature departure from New York completes a disappointing season at the majors for Stosur; she lost in the second round of the Australian Open and in the third round at both the French Open and Wimbledon.

Rogowska no match for Errani

Earlier in the day, Rogowska was blasted out in the first round by fourth-seeded Sara Errani, 6-0 6-0.

The 22-year-old, who fell in the final round of qualifying but made it through to the main draw as a lucky loser, had no answers to the Italian’s game.

In hot conditions, Rogowska ran herself ragged but was double-bagelled in just 51 minutes.

Errani, one half the world’s No.1 women’s doubles team, finds herself next up against countrywoman Flavia Pennetta in the second round.