Johanna Konta was knocked out in the first round of the Cincinnati Open in a blow to the British number one's US Open preparations.
Karolina Muchova of the Czech Republic beat Konta 3-6, 7-6 (7-5), 6-2 in a strong first-round performance.
The match was briefly interrupted during the second set due to rain, with Muchova setting up a meeting with Bianca Andreescu in the second round after the resumption.
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Konta had taken the opening set with a composed showing but relinquished the second in a tight tie-break.
Muchova, who has reached the semi-finals of the Australian Open and quarter-finals at Wimbledon this year, produced the better tennis in the decider to progress in a come-from-behind victory.
It continues a frustrating summer for Konta, who missed both Wimbledon and Tokyo 2020 due to Covid-19, and was forced to withdraw from the third round in Montreal last week due to a knee injury.
Elsewhere, Cameron Norrie's bid to become British number one with a run to the quarter-finals in Ohio fell at the sizeable feet of John Isner.

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Isner also fought back from a set down with a typically forthright serving performance, hitting 26 aces in the first round match to win 4-6, 7-6 (7-5), 6-4.
The 22nd of these took Isner beyond the 13,000 career ace mark, joining Ivo Karlovic (13,709) in an exclusive group of big servers.
The American will face Italian rising star Jannik Sinner next at the Western and Southern Open.
There was better news for another British tennis hope two states to the west, with Emma Raducanu felling top seed Alison van Uytvanck (Belgium) in Chicago.
The 18-year-old won in straight sets (7-6 [9-7], 6-3) and will face Clara Burel in the second round at the Challenger Series event.
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