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.
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.
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"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."
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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.
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