Shawn Mendes took his first step in navigating the tricky transition from teen heartthrob to adult artist at Madison Square Garden Saturday night to the adoring shrieks of his fans.

The unusual concert was the first time he played several songs from his upcoming “Illuminate” (Island) album due out Sept. 23, and his last headlining gig in America until next summer. And it was designed to show how much the 18-year-old singer-songwriter has grown since his breakthrough as a Vine sensation playing alone on an acoustic guitar.

His MSG show was his biggest production yet, complete with a full four-piece backing band and a massive blue orb that hung over the center of the floor and a small second stage where he played a handful of songs in the middle of the set. But Mendes easily commanded attention with his stronger stage presence and more powerful voice, especially as he delivered his more grown-up material.

“Lights On” was the biggest departure, with its young John Mayer vibe and discussion of how he wants to “love you with the lights on” and requests of “I want to see every inch of you.” However, that’s as racy as the Canadian teen gets and the other songs from “Illuminate” are more of a development of his style rather than a reinvention. The bluesy “Ruin,” which, like several of Mendes’ hits, was co-written by Valley Stream native Ido Zmishlany, features his most intense delivery yet, as well as a Mayer-like guitar solo. The current single “Treat You Better,” which reunites him with co-writer and Oceanside native Scott Harris, is a full-band workout that adds depth to his live show.

There’s a bit of Chris Stapleton’s “Tennessee Whiskey” baked into the throwback soul of “Don’t Be a Fool,” which Mendes dedicated to his parents, and a bit of Jason Mraz cleverness in the yearning “Three Empty Words.”

Some of those more grown-up references come with risks, but the reaction showed that Mendes’ fans were ready for it.

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“This is incredible,” he said near the end of the show. “This is everything I’ve ever dreamed of. I really couldn’t ask for more.”

SET LIST: Something Big >Lose Yourself / The Weight / A Little Too Much / Treat You Better / Lights On / I Don’t Even Know Your Name / Kid in Love >I Want You Back / Bad Reputation / Ruin / Life of the Party / Three Empty Words / Like This / No Promises / Don’t Be a Fool / Mercy / Never Be Alone // ENCORE: Stitches