The Queenstown-born-and-raised entertainer said he had gotten ''in the zone'' and stayed there.
Marty Newell, the director, rose from his seat, walked over to the actor and gave him a hug.
''He got to play Jesus 15 years ago, so he knows what you have to draw on and give that particular song,'' Brentwood said.
''There's a lot of high-pitched notes - it's a workout for the vocal chords.''
Brentwood also knew what it took to play Jesus in the Broadway hit created by Andrew Lloyd Webber and Tim Rice.
It was his performance for the Taieri Musical Society production two years ago which revived his passion for musical theatre after a break of more than three years, he said.
The New Zealand Broadcasting School graduate returned to the Queenstown arts scene after a decade in La Cage aux Folles last year.
An intensive two months' rehearsing and two months' performing at the Court Theatre in Christchurch over the summer in The Mikado convinced him the stage was where he belonged.
The 23-year-old singer-songwriter-guitarist hails from a family with a long involvement in the performing arts.
He and his sister Isla play as ''Brentwood'', and their song Something New was voted third favourite by the audiences of the original music competition Songstars in early April.
''There's no better feeling than pouring your heart out, if that's the kind of song, and becoming that person somebody else has written,'' Brentwood said.
Brentwood, opposite Paul Halsted as Judas and Lisa Moore as Mary, plus a cast of more than 30 Wakatipu performers, will explore the depths of their characters more fully once rehearsals move from the Showbiz rooms to the Queenstown Memorial Centre in the next few weeks.
Brentwood said the reimagining of the rock opera from 1971 into a modern post-Occupy Wall Street world would be unlike anything Queenstown audiences had seen before.
''It's just another way of looking at things,'' Brentwood said.
''While there's definitely a religious element to it, you don't have to think about it that way. It's all your own perspective. You can see it from Jesus' or Judas' side.
''Everyone knows the show because it's one of the most told stories, but it's the journey, how different can we make it, and that's what people will enjoy.''