Former champion Sam Stosur crashed out of the US Open after a three-set defeat to American teenager Victoria Duval.
Stosur, who beat Serena Williams to win the title at Flushing Meadows only two years ago, bowed out 5-7 6-4 6-4 against the 17-year-old qualifier.
However Stosur, the 11th seed, was her own worst enemy as she committed 56 unforced errors and 10 double faults.
"I think she played well, but I think I certainly helped her along the way," the Australian said.
Duval, who will face Daniela Hantuchova in the second round, had trailed 4-2 in the second set before she showed her fighting spirit.
Duval's father was dug out of the rubble of the 2010 Haiti earthquake, while at the age of seven, she was held hostage at her home by gun-wielding thieves along with her cousins.
"I'm very goofy off the court," Duval said. "I think I'm very much a child at heart. But on the court you have to be a warrior because that's just the sport we are in."
Second seed Victoria Azarenka produced a statement of intent as she whitewashed Dinah Pfizenmaier 6-0 6-0.
Azarenka, who lost in last year's final, needed just 64 minutes to book a second-round clash with Aleksandra Wozniak. - a 7-5 7-6 (7-5) winner over Vesna Dolonc.
"It was a lot closer than the score [suggests]," Azarenka said. "I felt I really played well in the important moments.
"I felt I served pretty consistently. From here it's important to improve."
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