Title favourite Novak Djokovic was sensationally defaulted from the US Open after hitting a line judge with a ball.
The top seed and 17-time grand slam champion had just dropped serve to trail Spanish opponent Pablo Carreno Busta 6-5 in the opening set of their fourth-round match on Arthur Ashe Stadium.
He hit a ball behind him in annoyance that hit a female line judge.
A lengthy discussion followed between tournament officials and Djokovic as the Serbian argued his case to no avail.
There was no question Djokovic did not intend to hit the line judge, and the ball was not hit particularly hard, but it was clear immediately that the woman was hurt, with the Serbian rushing over to check on her condition.
He pleaded his case at length before accepting his fate, collecting his rackets and walking off the court.
The decision will send shockwaves through the sport.
Djokovic won his 17th slam singles title in Australia and was an overwhelming favourite to make it 18 in New York, having not lost a match all season.
Meanwhile, Jennifer Brady swatted aside former US Open champion Angelique Kerber to reach the quarter-finals of a grand slam for the first time.
The 25-year-old American enjoyed a fine start to the year and has kept that going following the resumption of the tour, winning her first WTA title in Lexington last month.
She went into the tournament as a dark horse and has fully justified that, winning all her matches in straight sets, the latest a 6-1 6-4 victory over 2016 winner Kerber.
The 28th seed needed treatment at the changes of ends but she held things together mentally and physically to march across the finish line.
Brady said: "Wow, it feels great, I'm so happy. I played a spectacular first set.
"The second set I really just tried to focus on every single point. I was getting a little frustrated,
"I felt a little pain in my leg, but I just really wanted to close it out in two sets."
In the last eight, Brady will play another first-time New York quarter-finalist in 23rd seed Yulia Putintseva, who defeated eighth seed Petra Martic 6-3 2-6 6-4.