A dream came true for a 21 year old in Australia after he found himself filling in for a musician who had become ill during a performance of ‘La La Land in Concert’.

Sterling Nasa was watching the show at Sydney’s ICC Darlington Harbour when the Oscar-winning composer Justin Hurwitz addressed the audience in an extended interval to ask whether anyone was “an amazing sight-reader” who could play the piano. It’s understood Hurwitz had already tried to recruit a replacement, but they couldn’t get to the theatre in time. He told Guardian Australia it had been a gamble, but he “figured nobody’s as close as they say they are … so I just thought, well, we have 2,500 people in here”.

Nasa’s friend, who was sitting alongside him persuaded him to volunteer and within minutes he was on stage. Horwitz showed him the instrument, a celeste, which is also known as a bell-piano.

Up to then, Nasa, who is a student at the University of Sydney, had only played at his local church and old school. But he rose to the challenge, even improvising part of one of the songs: “The only one that caught me a little bit off guard was the solo in the [John Legend song] Start a Fire.

“It’s a very technical solo that Ryan Gosling plays. I saw it on the page and I thought, ‘I’m not going to be able to sight-read this’, so I took the liberty and just completely improvised the solo.”

He said the experience, which was met with rapturous applause, had been “really fun."

“It’s one of my favourite movies," Nasa said. "I was happy just sitting in the audience, let alone with what happened. It was going to be a good night either way.”

Hurwitz agreed: “To be able to play a really cool solo in the right key, in the right scale, on the fly with no rehearsal – it was remarkable”.