Novak Djokovic’s charge to his 18th Grand Slam title ended on Sunday after the Serbian defaulted following his petulant swipe at the ball that hit a line judge in the throat that resulted in the world number one’s disqualification from the US Open.

The dramatic moment came when the overwhelming title favourite reacted angrily to going 5-6 down to Spain’s Pablo Carreno Busta in the first set of their fourth-round encounter at an empty Arthur Ashe Stadium.

What would have been an innocuous incident had the ball flown a foot either side of the official instead left her lying on the ground, clutching her throat and screaming in pain.

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There was no question that Djokovic hit her inadvertently, and he quickly rushed to apologise, but it was a clear breach of Grand Slam rules forbidding the physical abuse of anyone within the tournament precincts.

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Tournament referee Soeren Friemel came out and spoke to chair umpire Aurelie Tourte and Andreas Egli, the Grand Slam supervisor, before a long chat with the three-times US Open champion.

Djokovic, who was clearly making the point that he had not intended to hit the official, was overheard saying “she doesn’t have to go to hospital for this” but after 12 minutes of pleading his case his fate was sealed.

“I don’t think that there was any chance of any opportunity or any other decision than defaulting Novak,” Friemel later told reporters.

“The facts were so clear and so obvious … (the line judge) was clearly hurt and Novak was angry, he hit the ball recklessly, angrily back.”

A tournament spokesman told Reuters the line judge appeared to be okay and was “not brought off-site”. Her identity is not known. Djokovic eventually walked over to shake hands with a stunned Carreno Busta and trudged off the court before leaving the grounds without attending a press conference.

The 33-year-old Serbian later posted an apology on Instagram.

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This whole situation has left me really sad and empty. I checked on the lines person and the tournament told me that thank God she is feeling ok. I‘m extremely sorry to have caused her such stress. So unintended. So wrong. I’m not disclosing her name to respect her privacy. 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. I apologize to the @usopen tournament and everyone associated for my behavior. 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. Cela ova situacija me čini zaista tužnim i praznim. Proverio sam kako se oseća linijski sudija, i prema informacijama koje sam dobio, oseća se dobro, hvala Bogu. Njeno ime ne mogu da otkrijem zbog očuvanja njene privatnosti. Jako mi je žao što sam joj naneo takav stres. Nije bilo namerno. Bilo je pogrešno. Želim da ovo neprijatno iskustvo, diskvalifikaciju sa turnira, pretvorim u važnu životnu lekciju, kako bih nastavio da rastem i razvijam se kao čovek, ali i teniser. Izvinjavam se organizatorima US Opena. Veoma sam zahvalan svom timu i porodici što mi pružaju snažnu podršku, kao i mojim navijačima jer su uvek uz mene. Hvala vam i žao mi je. Bio je ovo težak dan za sve.

A post shared by Novak Djokovic (@djokernole) on

“This whole situation has left me really sad and empty,” he wrote. “I’m extremely sorry to have caused her such stress. So unintended. So wrong.

“I apologise to the (US Open) and everyone associated for my behaviour.”