Australia|Out of the Audience, Into the Orchestra: Aspiring Musician Saves the Show

When Sterling Nasa, 21, woke up on Saturday he could not have imagined he would soon be performing in front of 2,000 people.

On that day — which he described as “run-of-the-mill” — he helped a friend with a student film and drove around town to run some errands. Later on, he was planning to watch the movie “La La Land” accompanied by live music at the Darling Harbour Theater at a convention center in Sydney, Australia.

But by the evening, this regular day had turned into a once-in-a-life time opportunity.

“I’ve obviously hit the algorithm to some degree,” he said of his newfound internet celebrity. “I don’t think I’ve fully rationalized it yet.”

The commotion started during an interval after the first half of “La La Land,” the 2016 musical that centers on the love story of the aspiring actress Mia (Emma Stone) who meets the ambitious musician Sebastian (Ryan Gosling).

The crowd was starting to realize that something was amiss when the interval went on for longer than they expected and Justin Hurwitz, the Academy Award-winning composer of the film’s score, came onstage.

“Is anybody like an amazing sight reader?” Mr. Hurwitz asked the crowd, adding that one of the musicians had fallen ill and had to go home. For the show to go on, he needed someone to step in on the keyboard.