Diego Schwartzman was forced to retire with severe cramping against local favourite John Millman.
The pint-sized Argentinian player had doubled up in agony due to heat exhaustion amid searing 30 degrees-plus temperatures.
He was placed in a wheelchair before being stretchered off the court and was taken to the Melbourne Park medical centre for treatment.
Schwartzman had won the first two sets 6-3, 7-5 but the Australian rallied to take the next two against his tiring opponent who was trailing 5-0 in the decider. He began to concede a few games before being unable to stand up.