The 14-year-old English singer -- who has become one of the season's fan favorites and clear frontrunners for her bombastic stage presence and incredible, soulful voice -- took to the stage during the second week of the AGT semi-finals and delivered a powerhouse performance.
The songstress belted out an incredible performance of the Steppenwolf classic "Born to Be Wild," and captivated the crowd as she danced, pranced and rocked out on the stage.
Displaying the kind of voice that makes you seriously wonder if she might be possessed by the ghosts of late funk music icons, Hadwin stole the spotlight once again, and left Mandel and judge Simon Cowell absolutely stunned.
"I can't sit down!" Mandel said, as he excited paced near his chair after her performance. "You were born to be wild. This was wild. You're amazing… My prediction is you are going to win America's Got Talent 2018."
While Mel B and Heidi Klum praised Hadwin for her unique personality and masterful vocal stylings, they both said they felt she was missing some of the boundless confidence of her previous appearances, and that perhaps the pressure of the semi-finals had shaken her nerves.
However, Cowell argued that it's her rawness that has made her such a fan favorite.
"None of your performances should be perfect because that's what you're all about," Cowell shared. "You're this bundle of excitement, and it's raw and it's messy, but that's what makes you great."
"I saw you before at the beginning of the show, backstage, shaking like a leaf, then you come on stage and you turn into a maniac," Cowell added. "That's why I absolutely love you, Courtney."
ET's Denny Directo spoke with Cowell after the show, and the judge explained why Hadwin's unpredictable and rough-around-the-edges persona is what makes her such a contender.
"You know, you just feel with her that she does whatever she feels like on the night which is what I like about her," Cowell said. "She's not a puppet, because that's boring and she's exciting."
As for Mandel, the judge who gave Hadwin her golden buzzer weeks ago couldn't be more confident in his decision.
"I don't want to sit down till the finals because I think she's going to have the confetti going for her one more time," Mandel told ET.
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'America's Got Talent': 13-Year-Old Singer With Social Anxiety Shocks the Audience With Her Soulful Voice
As to why he feels Hadwin has connected with viewers so strong, Mandel said it's all to do with how she doesn't overthink what she's going to do, she just goes out and lets the music take over.
"That's why she's different than anybody her age, anybody in music right now," Mandel said. "[It's] just, 'You do you!' And that's what I say to Courtney. She's just amazing."
When Hadwin isn't on stage belting out performances with the kind of bravado and passion that gets her compared to Janis Joplin, she's a painfully shy and socially awkward young woman, and that juxtaposition -- as well as her newfound fame -- is something she's had a tough time reconciling in recent weeks.
Hadwin explained how she usually comes up with light choreography for how she'd like to dance during a performance, but it often turns to improv. "When I'm on stage and I feel the music, it kinda sometimes just changes," she explained.
Check out the video below to hear more from Hadwin about her AGT journey.
Fans will find out if Hadwin makes it to the finales during the America's Got Talent results show, which kicks off Tuesday at 8 p.m. on NBC.