Charlie Fry, 25, who moved to Sydney two months ago for work, was surfing at Avoca beach north of the city on Monday when the shark leapt out of the water and bit his arm.
He said he heard a “massive thud” and initially thought it was a friend playing around.
He said: “I turned to the right and I saw a shark’s head come out of the water with its teeth and I just punched it in the face.
“I got back on my board, shouted at my friends who were there and then managed to catch a wave in.
“So it was a bit of a close call.”
Dr Fry, a novice surfer, learned the escape technique from a YouTube video featuring an interview with Mick Fanning, an Australian who famously punched a shark to survive an attack during a surfing competition in South Africa in 2015.
He said: “Me and my friends have just started surfing, and we saw the YouTube clip of Mick Fanning saying he punched a shark in the nose.
“So when it happened I was like, ‘Just do what Mick did, just punch it in the nose’.”
He added: “If you are watching or listening, Mick, I owe you a beer.
“Thank you very much.”
Dr Fry was treated in hospital for minor scratches and bite wounds.
A rescue helicopter service later spotted a 10ft bronze whaler shark near the site of the attack – a section of the beach known as “shark tower”.
Authorities closed the beach at Avoca and said surrounding beaches would be “closely monitored”.
“I didn’t feel the teeth going in, it felt like I was smacked, it felt like a hand, a hand grabbing me, shaking me,” Dr Fry said.
“I didn’t really notice it at the time, because when you’re surfing, all I was thinking was ‘I’m about to die’, and I was just thinking about getting in [to shore] as fast as possible.
“You just ride the wave as long as you can and start paddling for your life.”
He has not been put off surfing but plans to return when the bite heals but to a different spot.
“It is called ‘shark tower’ for a reason, so I will probably just go somewhere else.
“The surf was rubbish yesterday, so it wasn’t even worth it.”
Australia has had a spate of shark attacks in recent years, including one fatality and ten injuries this year.