Katie Boulter lost nine games in a row on her way to a first-round exit at the Cincinnati Open, the British No 1 collapsing to a 2-6 6-0 7-5 defeat to Poland's Magda Linette.
Boulter started the match superbly, immediately breaking Linette's serve twice to race into a 4-0 lead on her way to taking the opening set.
But, suddenly, from a position of such dominance, Boulter would win only eight points the entire second set as Linette bageled the Brit inside 25 minutes to level the match.
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The Pole, ranked 43rd in the world - 13 places below Boulter - maintained her dominance into the third set, swiftly securing a fourth-straight break of serve to move 3-0 up.
Boulter would mount a mini comeback after finally stop the rot in the fourth game, eventually breaking back to level things up at 4-4 in the decider - before then saving two match points when serving down 5-4.
But Linette would convert her third match point two games later to avoid a deciding tie-breaker and she'll now face either 10th seed Liudmila Samsonova or Wang Xinyu in the second round.
Fellow Brit Harriet Dart also was also knocked out after winning the first set, similarly collapsing to a 4-6 6-0 6-1 defeat to Yulia Putintseva of Kazakhstan.
Dart made a strong start having come through qualifying to reach the main draw but was unable to maintain her level against the World No 34.
Donna Vekic was defeated in her first match since winning a silver medal at the Olympics, falling to Ashlyn Krueger 5-7 7-6 (7-4) 6-2.
Krueger played her way into the field through the qualifying rounds, where she defeated Naomi Osaka. The American then opened her first appearance in the main draw in Cincinnati by knocking off Vekic, the 16th seed from Croatia who lost to Zheng Qinwen in the women's gold-medal match in Paris .
Top seed Iga Swiatek headlines the women's action on Wednesday as she takes on France's Varvara Gracheva.
Musetti and Tiafoe set up second-round clash
In the men's draw, Wimbledon semi-finalist Lorenzo Musetti and the USA's Frances Tiafoe set up a mouth-watering second-round match-up after both came through their tournament openers.
Musetti, seeded 14th, beat Nicolas Jarry, the Italian coming from behind to win 4-6 7-6 (7-5) 7-6 (7-4), while Tiafoe made lighter work of Spain's Alejandro Davidovich Fokina 6-3 7-6 (8-6).
Brandon Nakashima upset 11th seed Taylor Fritz 6-4 4-6 7-6 (7-4), edging the all-American contest in a decisive third-set tie-break after two hours and 17 minutes of action.
American 12th seed Ben Shelton also came through against countryman Reilly Opelka, triumphing 7-6 (7-3) 7-6 (7-3) after getting the better of a couple of tie-breakers.
World No 1 Jannik Sinner begins his campaign on Wednesday, taking on American Alex Michelsen, while fourth seed Daniil Medvedev and ninth seed Stefanos Tsitsipas also play their opening matches.
Britain's Jack Draper plays his opening-round match against Spain's Jaume Munar.
What's coming up on Sky Sports Tennis?
In the run-up to the final Grand Slam of 2024 - the US Open - you can watch all of the biggest tennis stars in action live on Sky Sports as they compete across the hard-court season.
- Cincinnati Open (ATP 1000) - 12-19 August
- Cincinnati Open (WTA 1000) - 13-19 August
- Winston-Salem Open (ATP 250) - 18-24 August
- Tennis in the Land, Cleveland (WTA 250) - 18-24 August
- Abierto GNP Seguros, Monterrey (WTA 500) - 19-24 August
- US Open (ATP/WTA) - 26 August - 8 September
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