Standing on stage in a baggy white hoodie, shorts and sneakers, Eilish seems unassuming. But when she jumps like she's on a trampoline or dances like the beat is possessing her body, she is truly electric, moving like some weird cross between Stevie Nicks and DJ Khaled's hype man.
The top end of the set was filled with crowd pleasers like Strange Addiction, You Should See Me In A Crown and her hit Khalid duet Lovely, which saw the young star tear up on stage.
She later moved on to more stripped back performances for the likes of I Don't Wanna Be You, Watch and Xanny, which fully showcased her insane and apparently unshakeable vocal talent, performing perfectly despite clearly sounding a little under the weather when she spoke.
She made small performance decisions to add another level to her performance, like distorting her vocals by positioning her mic on When I Was Older, laying on the ground for Ilomilo, lounging front of stage for Listen Before I Go and having her brother join her there for I Love You.
It was not lost on Eilish how far she's come; many times throughout the show she was forced to hold for applause, at one point becoming so overwhelmed by emotion her brother/producer Finneas joined her front of stage to comfort her.
A clearly humbled and emotional Eilish told the crowd: "This is f***ing crazy. No, for real, I'm standing here trying to think if this is a dream or not because my dreams be tripping sometimes and this seems like one of my dreams.
"There ain't no way this is real. I'm not even gonna get into it because I'm gonna break down…"
When it came time to play her hit When The Party's Over, she reminisced on exactly how far she'd made it, recalling how she performed it for the first time at the Tuning Fork - "literally right next door - that's like a 200-capped venue. And now I'm about to do it for 10,000 of you."
She later added: "I just wanted to say how unbelievable this is and how unbelievably grateful I am for this, for you. This is our first show on this tour and I don't know how it's gonna get better from here."
Honestly, we were all thinking that ourselves. Was it a pop show, a hip hop gig or a multi-media art piece on the inner workings of Eilish's mind? Who knows? But damn it was cool as hell, and a masterclass in well and truly making it.