Britain's Alfie Hewett was beaten 6-2 4-6 6-3 by France's Stephane Houdet in the US Open wheelchair singles final.
Hewett had hoped to add the title to the doubles trophy he won on Saturday.
But Hewett, who won his maiden Grand Slam singles trophy at the French Open this summer, succumbed to fatigue.
Hewett, 19, beat compatriot Gordon Reid in a three-hour semi-final on Saturday before teaming up with the Scot to defeat 46-year-old Houdet and Nicolas Peifer in the doubles final later on.
"Congratulations to Steph for a great final," said Hewett.