The 20-year-old model performed the Backstreet Boys' 1999 rock-pop anthem Larger Than Life, with a guest appearance from members A.J. McLean and Nick Carter. Clad in a shiny black leather cleavage-baring cat suit, she absolutely nailed her badass performance—right down to McLean's maniacal laugh at the beginning of the song.
She also performed the 2008 song "That's Not My Name" by The Ting Tings," during which she slapped Posey playfully. But it was her Backstreet Boys collaboration that earned her the most praise.
"It's so crazy!" Hadid said after being named the winner, wearing the massive Lip Sync Battle championship belt, which could fit at least two of her.
"It's so much fun," she said. "I wish I could do it a million times over and over and over again. I would come back 100 times."
Meanwhile, Posey, 24, lip-synced two one hit wonders: The more outdated 1985 a-ha hit, "Take on Me," during which he took part in a cheesy '50s-style dance routine with a female dancer, and Harvey Danger's 1997 song "Flagpole Sitta."
Hadid said she and the Teen Wolf actor did not know each other before competing on Lip Sync Battle but bonded on the set. In addition to slapping his face and kicking his butt, she got to playfully slap his behind as well.
"You deserve it," Posey told the model after her win. "That was the coolest thing I've ever seen."