For nearly eight months he was Novak Djokovic the Destroyer, winning 57 of 58 matches and nine championships, including two grand slams, and surging to No 1 in the world.
Then came a reckoning of body and, perhaps, soul at the Ohio River metropolis of Cincinnati, where he first conceded feeling fatigued and a few days later walked away from the final of the Western and Southern Open, citing an aching right shoulder, an injury that gave the championship to Andy Murray and revived US Open hope for a men's tour Djokovic had beaten nearly into submission.
He said he had felt pain in his right shoulder for 10 days, and against Murray he was unable to play through it, as he had in difficult victories over Gael Monfils and Tomas Berdych.
Djokovic's hope is that he has time enough to recover for the year's last grand slam, the US Open at Flushing Meadows beginning next week.
"The good thing is there's a week, eight days to the start of the Open," he said after quitting against Murray. "I'm confident I can recover and be ready for the US Open."
The injury destroyed his serve and limited his forehand. He said: "I could have maybe played another couple of games, but what for? I cannot beat a player like Murray with one stroke."
Djokovic's problems are bigger than his shoulder. He conceded last week to feeling "quite exhausted after playing so many matches" this year, a result of having reached the final in 10 events and the semi-finals in the 11th.
His big year featured not only the pursuit to supplant Rafael Nadal at the top of the rankings; it also included his beating back every challenger below him in the world order.
Considering he had not yet lost on a hard court this season, Djokovic a few days ago was the heavy favourite to win the US Open, a major that he has yet to win, although he does have a good record there having reached the final in 2007 and 2010, losing to Roger Federer and Nadal respectively, and reaching the semi-finals in 2008 and 2009.
But with an aching shoulder and diminished energy, he might now be vulnerable to challenges from Nadal and Federer, as well as Murray and Berdych, when the action starts next Monday.
Mardy Fish, ranked No 8 in the world, could also trouble Djokovic, especially with a partisan New York crowd behind the American player.
Djokovic at the height of his powers has been overpowering this year.
We may soon learn how good he is when he plays at something less than his best.
The National Sport
& Paul Oberjuerge on