(CNN) -- World number one Novak Djokovic suffered only his second defeat in 2011 as a shoulder injury forced him to quit his Cincinnati Masters final against Andy Murray on Sunday.
Djokovic was clearly struggling with the problem as he lost the first set 6-3 to the British number one.
And, following a lengthy time out to have his shoulder treated, the Serb lost his serve twice in quick succession to go 3-0 down in the second set, prompting him to call it a day.
The result gives fourth seed Murray the Cincinnati title for a second time, following his win in 2008.
It also ensured Murray becomes only the second player in 59 matches to beat Djokovic this year, the other being Roger Federer in the semifinals of the French Open.
It also ends Djokovic's winning streak of 31 matches on hard courts.
Murray told reporters: "Obviously when he started to slow down his serve toward the end of the first set it was going to be tough for him.
"Sometimes things can warm up when you play, sometimes they get worse. I just tried to stay focused," he continued.
On becoming just the second man to defeat Djokovic this season, Murray said: "I had a chance when I served for the match against him in Rome and lost, that was a tough one for me.
"It's nice to win, but I'd rather beat him in three weeks' time in New York," he added.
The victory puts Murray in good heart prior to the final grand slam event of the year, the U.S Open, which starts in eight day's time.
But Djokovic's participation may now be in some doubt if he fails to respond to treatment on his shoulder during the next week.