Having crashed out at Wimbledon in June the Scot did not find her best form until the US Open in August, when she won her first ever main draw match at Flushing Meadows by beating, ironically, Martic.

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Vandeweghe defeated Italy's Tathiana Garbin 6-4 6-4 for her first victory in a WTA Tour main-draw match.

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Last year, he became the first U.S. junior champion in decades to win a match in the main draw.

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Azarenka's withdrawal allowed 19-year-old Lauren Davis into the main draw, and she took her chance -- saving three match points against Madison Keys before beating her fellow American 6-1 5-7 7-6 (9-7) in the second-round match.

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"It'll be my first time in the main draw of these events and I'll just be taking it one match at a time when I'm out there, " she said.

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In the only other first-round match on the opening day, Spain's Conchita Martinez ousted the only German player in the main draw, wild card Anna-Lena Groenefeld, 7-6 6-2.

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