World number one Novak Djokovic pulled out of A Day at the Drive Adelaide exhibition before returning to play a set anyway.
The world number one was set to play Jannik Sinner but withdrew with a blistered hand just minutes before he was due out in front of the 4000-strong crowd.
His practice partner Filip Krajinovic took his place and won the first set 6-3, but Djokovic came back out on court for the second set to wrap up a 6-3 6-3 win.
Murray set to practice with Djokovic in Rome ahead of latest comeback
Djokovic 'sorry' for bizarre substitution
"I'm sorry that I didn't step in on the court from the beginning," said Djokovic.
I had to do some treatment with my physio, I wasn't feeling my best for the last two days and I didn't know how I was going to react.
"It's not easy but it's part of what we do, we're professional athletes, we learn over the years to play with the pain.
- Australian Open 2021: Who's in, who's out, what is hard quarantine?
- Djokovic is our LeBron, but he needs to be accountable
"It's just a case of whether that pain is bearable or not. Obviously, coming off a hard training block and having the ATP Cup and Australian Open coming up you don't want to risk it too much."
Djokovic pulls out of match at the last moment - makes shock return
Djokovic and Krajinovic will join forces once again as Serbia defend the ATP Cup in Melbourne next week, before Djokovic embarks on his quest for a ninth Australian Open title on Feb. 8.
The 2021 Australian Open is live and exclusive on Eurosport. You can watch every moment on eurosport.co.uk and the Eurosport app.
Norrie showing quality on clay - but how far can he go?
Djokovic withdraws from Madrid Open