The Socceroos were playing Peru in their qualifying play-off for Qatar 2022 and clinched victory in a dramatic shootout.
The match ended goalless after 120 minutes and Australia boss Graham Arnold made the bold call to take off Mat Ryan and bring on Redmayne for the spot kicks.
It was just his third international cap and that decision proved to be a decisive one as he saved Alex Valera's spot-kick to clinch a 5-4 victory.
Australia's Martin Boyle saw his opening penalty saved, but Peru's Luis Advincula hit a post with his and, with the other nine all converted, Redmayne's save from Valera's effort booked their place at the World Cup.
The Sydney FC goalkeeper has a distinctive style when facing up to penalties, dancing on the goal line even more than Liverpool legend Bruce Grobbelaar, and he has earned the nickname 'the grey wiggle'.
He also appeared to notice the Peru goalkeeper had penalty instructions written on his water bottle, so after the first spot kick Redmayne threw it into the stands.
"The longer the camp went on the more comfortable I felt with this scenario," Redmayne said.
"I don't think any of the players knew about it, a few clocked on at half-time because I went through a few drills to keep the eye in.
"Maty [Ryan] was full of support coming off and then just before penalties as well, he was pumping me up and getting me ready. Maty didn't know. He said: 'all the best mate, this is your time'. Even at full-time [at the end of extra-time] when we were in a huddle he said: 'you've got this mate, this is all you'. He was nothing but supportive, he's an absolute legend."
Redmayne's story is a fascinating one and even went on trial with Arsenal when he was a teenager.
In 2005, he was selected in a New South Wales Institute of Sport side to play a friendly against the Gunners.
This resulted in a two week trial and he impressed the club, but they ultimately decided to sign Wojciech Szczesny.
Fast forward 12 years, he came up against Arsenal in a friendly with Sydney FC and seriously impressed, leading Arsene Wenger to admit that he possibly made a mistake.
"If he was with us, we made a mistake," Wenger said when told about Redmayne's time at Arsenal.
"At the end of the day I would say their goalkeeper was man of the match."
The goalkeeper also came very close to giving up football all together after struggling to catch a break in his career, even taking a barista course.
He stuck with it and has now made himself a household name in Australia as they booked their place at the World Cup.