Novak Djokovic was dramatically disqualified from the US Open on Sunday after striking a female lines judge with a ball in frustration during his last-16 match, sending shockwaves through the tournament.
The world No 1 hit the ball in disgust after losing his serve to go 6-5 down in the first set to Spain's unseeded Pablo Carreno Busta inside Arthur Ashe Stadium.
Djokovic appeared to be looking the other way when he pulled the ball from his pocket and smacked it in the direction of the official, it hitting her full toss in the throat.
The official cried out and began gasping for air as she collapsed to the ground.
Djokovic rushed over to her to check if she was okay and placed his hand on her back as she struggled for air. After a few minutes she got up and walked off the court looking dazed.
Around ten minutes of discussions then ensued between Djokovic and the tournament referee, during which the world No 1 pleaded his case.
The umpire then declared that Carreno Busta had won by default. Djokovic shook hands with his opponent before leaving the court without appearing to shake the umpire's hand.
He went then directly to his car and left the Flushing Meadows site in New York without speaking to reporters.
Carreno Busta said he did not see the incident.
"I was celebrating the break with my coach," he told reporters.
"When I heard that the line judge was on the floor I was in shock. I never expected this moment when playing Novak.
Carreno Busta added that the incident was "unintentional."
"I think it was bad luck," he said.
The Serbian star is one of only a handful of players to be disqualified from a men's singles tournament at a Grand Slam since John McEnroe was infamously tossed from the Australian Open in 1990.
Djokovic had been chasing an 18th Grand Slam title at the Billie Jean King US National Tennis Centre.
He was hoping to close the gap on Roger Federer and Rafael Nadal, both absent from the tournament, in the race for the all-time men's Slam singles title record.
Djokovic is on 17, with Nadal on 19 and Federer on 20.
The United States Tennis Association said Djokovic had been defaulted under the Grand Slam rules for "intentionally hitting a ball dangerously or recklessly within the court or hitting a ball with negligent disregard of the consequences."
The body added that he would lose all ranking points and prize money from the tournament.
A spokesperson said the line judge had been treated by medical staff and was "doing okay."
Former players reacted with shock at the disqualification but said officials had made the right decision.
"Right call!" former women's world number one Tracy Austin wrote on Twitter.
Four-time US Open champion Martina Navratilova said officials "had no choice" but to default Djokovic.
Former British No 1 Greg Rusedski described the disqualification as "unbelievable" but said officials had made the "correct decision".
"Novak should have stayed for the press conference & apologise," Rusedski wrote.
Djokovic had been the overwhelming favourite to capture a fourth US Open title.
His disqualification blows the men's draw wide open and means it will crown a first-time Grand Slam winner next Sunday.
"Now it gets interesting," said fifth seed Alexander Zverev, who described Djokovic as "very unlucky."
"There's no past Grand Slam champions left in the draw.
"It's going to be one of the young guys," who wins, Zverev added after becoming the first German to reach the US Open last eight since Tommy Haas in 2007.
Zverev, the fifth seed, bulldozed Spain's unseeded Alejandro Davidovich Fokina 6-2, 6-2, 6-1 in just 1hr 34 min.
In the women's draw on Sunday, 28th seed American Jennifer Brady stunned three-time Grand Slam winner Angelique Kerber and eighth seed Petra Martic was bundled out by Kazakhstan's 23rd seed Yulia Putintseva.
There was another upset too when unseeded American Shelby Rogers stunned sixth seed Petra Kvitova, winning 7-6 (7/5), 3-6, 7-6 (8/6.