A battling effort from Boulter was eventually undone after an epic final service game from Zheng which went to a sixth deuce before she took advantage of her sixth match point with an ace.

Boulter, herself, had six break point opportunities in the same game, having earlier raced out into a 0-40 lead, but she couldn't claim any of them as her tournament came to a close.

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After Zheng controlled the first set, Boulter broke serve for a 3-2 lead in the second but the British No 1 double-faulted twice in blustery conditions in the next to immediately give up the advantage.

Boulter was then broken for a second-straight game, her first serve continuing to desert her, and yet another double all but sealed her fate before she briefly threatened a comeback as Zheng served for the match.

It means that Boulter misses out on potentially facing fellow Brit Emma Raducanu in the third round. The former US Open champion plays Yafan Wang later on Thursday as she tries to book her place in the next round.

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