World No 1 Novak Djokovic was disqualified in the US Open fourth round on Sunday after hitting a female line judge in the throat with a ball in the first set of his match against Spain's Pablo Carreno Busta.
Djokovic was becoming frustrated after failing to take the opening set, suffering a fall and having dropped serve to trail 5-6.
He hit a ball fairly hard to the back of the court, striking a female line judge.
Djokovic immediately apologised and stood over her before becoming involved in a lengthy exchange with the tournament referee.
In a statement on Instagram only hours after his sensational exit in New York, the Serbian world No 1 said he had been left "really sad and empty" by the controversy.
"I checked on the lines person and the tournament told me that thank God she is feeling ok," he wrote.
"I'm extremely sorry to have caused her such stress. So unintended. So wrong."
Under the rules of the game there is no option other than a default and despite him pleading that he had not meant to hit the official, he was eventually disqualified.
"As for the disqualification, I need to go back within and work on my disappointment and turn this all into a lesson for my growth and evolution as a player and human being," he said.
"I apologise to the @usopen tournament and everyone associated for my behaviour. I'm very grateful to my team and family for being my rock support, and my fans for always being there with me.
"Thank you and I'm so sorry."
After the incident, Djokovic shook hands with a stunned Carreno Busta and trudged off to face the music.
It was an incredible end to the top seed's hopes of winning an 18th Grand Slam title, which looked increasingly likely as the fortnight progressed.
"It's the right decision," British former player Tim Henman, who was disqualified from Wimbledon for a similar incident in 1995, told Amazon Prime.
"He is not aiming for the line judge, but has hit the ball away and you have to be responsible for your actions."