Sam Stosur out of US Open after first-round loss to American teenager Victoria Duval Samantha Stosur returns a shot to Victoria Duval during their women's singles first round match on day two of the 2013 US Open. Picture: Al Bello Source: Getty Images ALREADY coachless, Samantha Stosur is likely to fall out of the world's top 15 as well after slumping to her worst grand slam defeat at the US Open. The 2011 champion stumbled from a set and a service break up to fall 5-7 6-4 6-4 to 17-year-old world No.296 Victoria Duval at Flushing Meadows on Tuesday. In 41 career majors, Stosur has only ever lost to one opponent ranked lower than the American qualifier - and that was to the great Martina Hingis when the former world No.1 and five-time grand slam champion was on the comeback trail at the 2006 Australian Open. Stosur appeared on track for a second-round meeting with Daniela Hantuchova when she led by a set and 4-2, but Duval, a plucky baseliner who defied her lowly ranking, refused to yield and eventually prevailed on her fourth match point. Two years ago, Stosur upstaged all-conquering Serena Williams in the final in New York in the greatest triumph of her career. The 28-year-old had won 15 of her past 17 matches in the Big Apple since 2009. Stosur had also entered this year's event with confidence after winning nine of her 11 matches on American hardcourts over the US summer and ending a two-year title drought with a breakthrough victory over world No.2 Victoria Azarenka at the Southern California Open. Caronline Wozniacki has recorded a straight sets win in her first round clash at the US Open, while Aussie Casey Dellacqua has bowed out of the tournament. No wonder she struggled to digest her stunning defeat, or explain how it happened. "First round of the US Open is not a good feeling," Stosur said. I'm probably going to give a much worse answer right now than maybe a more logical or less emotional one tomorrow. You can't really fault her too bad. There were a couple match points - I hit a couple of winners. I'm sure she was nervous. But she held it together. She kept going for it. When she got the chance to step up and hit a winner, she did it, just like on match point. Credit to her. She did what she had to do. Ultimately, Stosur was undone by 56 unforced errors and 10 double faults and the Queenslander 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. Victoria Duval jumps for joy after defeating Samantha Stosur in the first round at the US Open, Stosur was playing her first match since splitting with long-time coach David Taylor just 11 days ago, but she refused to blame the untimely break-up for her loss. "It certainly wasn't the preparation I've been used to," she said. But everything happens for a reason. Things happen when they happen. I can't change it. I went into it. I was prepared as what I could be. Unfortunately, I got this result. Stosur's premature departure completes a miserable season at the majors after she lost in the second round of the Australian Open and in the third round at both the French Open and Wimbledon. She is poised to slip further down the rankings from No.11 after failing to defend her run to the quarter-finals at Flushing Meadows last year and the search is on for a new coach after working with Fed Cup captain Alicia Molik during her brief Open campaign. I guess now it's an opportunity to start doing that. Time will tell whatever happens," she said. Teenager Ashleigh Barty is the lone Australian left in the women's singles draw after Olivia Rogowska and Casey Dellacqua also lost on Tuesday. Relentless Italian fourth seed Sara Errani eliminated Rogowska 6-0 6-0 in just 51 minutes after Dellacqua lost 6-3 1-6 4-6 to Croatian Ajla Tomlijanovic. HOW THE AUSTRALIANS FARED ON DAY TWO OF THE US OPEN AT FLUSHING MEADOWS: Women's singles, first round 11-Samantha Stosur lost to Victoria Duval (USA) 5-7 6-4 6-4 Olivia Rogowska lost to 4-Sara Errani (ITA) 6-0 6-0 Casey Dellacqua lost to Ajla Tomljanovic (CRO) 6-3 1-6 4-6