Play was suspended for an hour at Rod Laver Arena, as Nigel Sears received treatment before being fitted with breathing apparatus and carried from the stadium on a stretcher.
The Australian Open tennis championships were rocked late on Saturday when Andy Murray's father-in-law Nigel Sears collapsed during a match at Rod Laver Arena, overshadowing the world number two's advance to the fourth round.
Sears, the coach of former French Open champion Ana Ivanovic, collapsed while watching the Serb's third-round clash against Madison Keys, prompting medical staff to rush to the 58-year old's aid.
Adding to the surreal atmosphere at Melbourne Park, Briton Murray was oblivious to the unfolding drama as he battled Portugal's Joao Sousa in the neighbouring Margaret Court Arena.
Play was suspended for an hour at Rod Laver Arena, as Sears received treatment before being fitted with breathing apparatus and carried from the stadium on a stretcher.
He was taken to hospital for further treatment and was being examined by a cardiologist, organisers said.
A teary-eyed Ivanovic was eventually led back to centre court to continue her match against Keys and although the Serb fought hard she fell 4-6 6-4 6-4.
"Obviously it was a tough match," Ivanovic said in a statement after declining post-match media commitments.
"I really wanted to win and have a chance to come back... Obviously a little bit disappointed."
Murray, whose wife Kim Sears is due to give birth to their first child next month, completed a 6-2 3-6 6-2 6-2 win over 32nd seed Sousa and was led straight from the court by an official rather than conduct the usual courtside interview.
In an unnerving coincidence, Ivanovic's second round match was also suspended after a spectator fell down the stairs at the same show court on Thursday.
Murray also skipped the post-match media conference and the Scot's only comment was confined to his match."It was tricky. I didn't feel great," he said in a statement.
"It was good to get through that one."
The medical emergency overshadowed the action on day six which saw Spanish third seed Garbine Muguruza dumped out of the tournament and Victoria Azarenka given a huge boost in her bid to win a third title at Melbourne Park.
The 2014 champion Stan Wawrinka also reached the last 16, staying on track for a blockbuster semi-final against Murray.
Muguruza, rated one of the few women capable of threatening champion Serena Williams, slumped out at the hands of unseeded Czech Barbora Strycova, her 6-3 6-2 loss punching a hole in the draw.
With Romanian world number two Simona Halep sent packing in the opening round, seventh seed Angelique Kerber remains the top woman in the draw's lower half.
But the path to a dream final against Williams seems laid out for 14th seed Azarenka.
A succession of injuries over the past two years and a bout of depression have slowed the Belarussian, who clinched back-to-back titles at Melbourne Park in 2012-13.
But her 6-1 6-1 humiliation of Japanese qualifier Naomi Osaka was her eighth win in succession and further evidence the sleeping giant has awakened.
"I had a lot of changes and emotions from last year that I still didn't know how to handle," the 26-year-old told reporters.
"It changed my life... Starting to be happy and organised and disciplined off the court, it changed my life on the court, definitely."
Following Roger Federer's 300th victory in grand slams on day five and Maria Sharapova's 600th on tour, Wawrinka notched his 400th career win with a triumph over Czech Lukas Rosol 6-2 6-3 7-6(3).
The Swiss fourth seed has been battling a cold at Melbourne Park but his game was in rude health as he smashed 18 aces and 45 winners in the late afternoon sunshine at Rod Laver Arena.
“As long as I'm feeling good on the court, that's the most important thing," a raspy-voiced Wawrinka said.
The 30-year-old Swiss must next weather the serving storm of Canadian dark horse Milos Raonic, who despatched Serb Viktor Troicki 6-2 6-3 6-4 at the Margaret Court Arena.
A quarter-finalist last year, 13th seed Raonic dedicated his win to victims of a school shooting in the remote Canadian town of La Loche, where four people were killed and a number injured on Friday.
"Stuff like this doesn't happen much back home," he told reporters.
"I'm sure not just in that small community but throughout Canada it was a lot of people that were sort of heartbroken over it."
With a number of high seeds falling by the wayside, doors opened for lesser lights to shine. Among them, Australia-born Johanna Konta defeated Czech Denisa Allertova 6-2 6-2 to become the first British woman into the last 16 at Melbourne Park in nearly 30 years.
Zhang Shuai, the last Chinese player left in the singles tournament, continued her fairytale run to reach the fourth round, having never previously been past the first round of a grand slam in 14 attempts.