British world number three Andy Murray suffered a surprise second-round defeat to unseeded Russian Teymuraz Gabashvili in the Washington Open.
Murray, 28, had chosen to play an extra tournament in the run-up to this year's US Open, which starts in New York on 31 August.
But after a bye to the second round, the top seed lost 6-4 4-6 7-6 (7-4) to the 30-year-old world number 53.
"It wasn't like I was blown off the court," said the Scot.
He will now play Masters events in Montreal and then Cincinnati in the next two weeks in preparation for Flushing Meadows.
Gabashvili hit 11 aces and had to break back at 5-4 down in the third set as Murray served for the match, before going on to win the tie-break.
"It was the first hard-court match for four-and-a-half months with only four or five days of preparation, so I was happy with how I moved and did certain things on court."
Murray helped Great Britain advance to the semi-finals of the Davis Cup last month.