The British number one lost 6-3 6-4 to Tomas Berdych in the Western & Southern Open and missed out on a semi-final against Rafael Nadal - hardly the ideal build-up for the defence of his title at Flushing Meadows.
Murray amitted he found the court conditions tough agauinst Berdych.
“The court was lively,” he said. “It was bouncing pretty high. It was quite tough to control the ball. I made too many errors.
“I’ll need to work on my groundstrokes a bit, make sure I’m not making too many mistakes going into the US Open.”
World number six Berdych had triumphed in the pair’s last encounter, at the Madrid Masters in May, but Murray defeated the Czech en route to his US Open win last year.
And it seemed the Wimbledon champion was at the top of his game after Berdych barely escaped his opening service game before Murray opened his account with four aces.
The two-time grand slam champion continued to pressurise his opponent’s serve, but Berdych held firm and then broke in the eighth game after Murray netted a forehand.
Berdych served to love to wrap up the first set and then staved off three break points in his next service game.
It proved to be a crucial hold as Berdych then broke 2008 and 2011 Cincinnati winner Murray in the next game at the second attempt.
Despite fleeting moments of quality, Murray failed to force his way back into the contest and a composed Berdych held his nerve to set up a clash with either Nadal, who beat old foe Roger Federer in three sets.
Murray has suffered early exits in both tournaments he has entered since his post-Wimbledon break, having been beaten by Ernests Gulbis in Montreal last week.