Allen kicked off the performance in a glittering silver coat and black pants, Cyrus then joined him for the collaboration.
Cyrus, 20, accessorized her look with a sparkly white hat, gloves and thigh-high boots.
Earlier in the evening, the singer arrived on the blue carpet wearing denim over an orange crop top.
The pair’s performance was introduced by Matchbox Twenty frontman Rob Thomas, who is one of Allen’s musical idols.
“Our next performance comes from two young artists who come from very different worlds,” Thomas said. “She grew up on her father's country hits, and he says my music helped inspire him. So, she took her country roots and they lent her to pop music, and he took his rock and pop and that got him all the way into country music.”
“So, we get to see what that sounds like when you put it altogether right now,” continued Thomas, who previously performed the Matchbox Twenty hit “Unwell” with Allen. “Please welcome Jimmie Allen and Noah Cyrus.”