The third round Australian Open match between Ana Ivanovic and Madison Keys was suspended for more than half an hour when the Serbian player's coach collapsed in the stands.
Play resumed at 8.40pm after a five-minute warm-up hit as Nigel Sears was taken to hospital in an ambulance.
Ivanovic drops out after coach collapse
Madison Keys beats Ana Ivanovic, after the match was delayed when the Serbian player's coach collapsed in the stands.
Keys went on to win the match 4-6, 6-4, 6-4.
A loud gasp went up from a section of the crowd when Sears collapsed on the stairs leading to her player's box.
Spectators quickly gathered around to offer assistance while officials and staffers raced to the incident.
Ivanovic and Keys looked on in concern from the court.
When it became clear that something was very wrong, the umpire climbed down from his seat and spoke to the players.
Soon afterward they left the court, Ivanovic with a towel draped over her shoulders, dabbing at her eyes and visibly distressed.
Play was suspended indefinitely while paramedics entered Rod Laver Arena.
Security officials appeared to clear several rows of spectators closest to the incident, before Sears was carried away in a stretcher to applause from the crowd.
The crowd was told the incident was "fairly critical", and that players were being consulted about proceedings.
Soon afterwards it was announced that they would resume the match.
Australian Open officials issued a statement saying a man in his 50s had fallen ill at Rod Laver Arena that evening.
"The match was suspended and the players updated on his condition. The players had the opportunity to consult with their teams and then went back on court," it read.
After the match, an announcer told the crowd Sears had asked for a television to be wheeled into his room so he could watch the end of the match.
"He's cracking the terrible jokes he cracks all the time ... he's fine," he said.
Sears is the father of Kim Sears, world number three Andy Murray's wife.
Murray was playing at the same time the incident occurred, in a match against Portugual's Joao Sousa.
He won the match 6-2, 3-6, 6-2, 6-2 and left without an on-court interview. It was unclear whether this was because he had been informed of the incident involving his father-in-law.
Kim Sears is pregnant with the couple's first child and is not in Australia for the Open.
Ivanovic made the final of the Australian Open in 2008 and was beaten by Maria Sharapova, but she won the French Open that year and spent a time ranked number one in the world.
She has struggled to find the same success since then, although she made the semi-finals of the French Open in 2015.
Neither Ivanovic nor Keys attended the usual post-match press conferences, and the written quotes from the players distributed by open officials did not address the matter of Sear's ill health directly.
Ivanovic said she felt supported by the crowd.
"I really wanted to win and have a chance to come back, the crowd was just really amazing," the quote read.
Keys will next face Chinese qualifier Shuai Zhang, who beat American Varvara Lepchenko in straight sets on Saturday night.
Earlier this week, Ivanovic said she was left shaken when she heard a spectator crashing down a set of stairs during her second round win over Anastasija Sevastova.
On that occasion, play was halted until the woman was taken away on stretcher.
"It was actually good that we had to wait a little bit because I was really shaking, because I could imagine and it was not so nice," Ivanovic said after the match on Thursday.
Ivanovic-Keys suspended indefinitely while Nigel Sears receives treatment from medics in stands. pic.twitter.com/y10pyTXU9h— Bryan Armen Graham (@BryanAGraham) January 23, 2016