Emma Raducanu's dominant form at the Cincinnati Open ended as seventh seed Jessica Pegula proved a sharp step up in class for the British number one.
Raducanu had trounced veterans Serena Williams and Victoria Azarenka, but lost 7-5 6-4 to Pegula in the last 16.
Now the 19-year-old switches her focus to defending her crown at the US Open, which starts in New York on 29 August.
Cameron Norrie continued the British interest by beating Ben Shelton to reach the men's quarter-finals.
British men's number one Norrie, seeded ninth, won 6-0 6-2 against the teenage American wildcard as the gulf between the pair showed.