BRITISH pop star Charli XCX’s Sydney sideshow — a pit stop during her Australian visit supporting Taylor Swift on her reputation stadium tour — came with no small amount of hype.

The quickly sold-out show at the relatively humble Metro (capacity: 1110, or roughly 1.3% of the crowd coming to see Taylor’s Sydney show next week) would be “a completely customised experience unlike anything before it,” her touring company trumpeted.

“Don’t miss out on this once in a lifetime opportunity!”

Did she deliver on those lofty promises? Well, those expecting to hear global hits like Boom Clap, Fancy or Break The Rules would’ve been disappointed — but in their absence, she instead gave us a bloody good pop show.

XCX’s fans are young — younger even that the 26-year-old singer herself, a fact made all-to-clear to this thirtysomething reviewer when she introduced current single 1999 by asking how many of those in the room were born in the 2000s.

The cheers were deafening, eliciting a weary sigh from Charli.

“You’re not old like me,” said the woman born in 1992.

The night focused on XCX’s two most recent longform releases, ‘mixtapes’ Number 1 Angel and Pop2, both filled with experimental, hyperactive bubblegum pop with a sinister edge — think Vengaboys meets The Cure.

The crowd knew every. Single. Word. Charli performed on a barren stage, only a DJ behind her, but she commanded a heaving mosh pit.

At one point, a woman sat in the bleachers hoisted her crutches aloft and waved them in time with the beat — it was that sort of gig.

Charli XCX was absolute joy pic.twitter.com/1hWojVVnGb — Nick Bond (@bondnickbond) October 23, 2018

Of course, Charli understood the real heart of her fanbase: Midway through the show, she delivered a heartfelt paean to the (overwhelmingly) LGBT members of the audience, announcing that with their support, “I can finally be myself.”

In her gigs, she explained, she hopes to create “a safe space … where everybody belongs.”

Mere lip service? As if. A few songs later, for viral hit Boys, she brought a glammed-up collection of local queers and queens on stage to prance and preen for their lives, generously giving the spotlight over to those who’d supported her.

It was a beautiful, “once in a lifetime” moment — and more than enough to make up for the absence of Boom Clap.

Charli XCX opens for Taylor Swift on her reputation Australian tour, with dates in Melbourne, Sydney and Brisbane in the coming weeks. Tickets through Livenation.