Krasinski took the stage first, setting the high-octane tone for the night. His song choice? "You know Jimmy Fallon thinks he's a real good friend of Justin Timberlake, but he ain't this good a friend 'cause I'm doing ['NSYNC's] 'Bye, Bye Bye'."
And Krasinski didn't hold back. He somehow managed to mouth the words to the classic tune while also (sort of) doing some marionette-like dance moves as inspired by the music video.
"I hurt my knee real bad," he shared after the performance. "That's a marionette that I do... it's kind of my thing," he added.
Kendrick was up next. "This song is from my heart and I'm excited to finally share it with the world," she said before keeping the boy band theme going with One Direction's "Steal My Girl."
Her swagged-out take on the Four track confirmed that she's likely a Directioner who has practiced performing the song in front of a mirror a few times. The real twist in the performance came when mid-song she flashed photos of Blunt on the screen behind her-- and even wore a t-shirt with her photo on it.
"It sort of hurts my heart," Krasinski said, meaning he went home with a hurt heart and knee by the end of the night.
"She was super excited... Yeah, Emily knows," Kendrick added. Krasinski's response to her jab? He did Kendrick's famous cups routine.
"Anna I just think that you're really special and tiny and adorable," Krasinski warned her backstage. "Eat it."
For his second performance, he kicked it old school with Tina Turner's "Proud Mary." For the song's intro, he rocked a suit. But, that didn't last long. As the song picked up steam, he pulled that tear-away suit off to reveal a sequined little dress was hiding underneath.
"Well can I be honest with you? I blacked out. How'd it go?" he shared afterwards.
Kendrick seemed unfazed by her competition in an interview filmed backstage. "I think that John should be afraid of me generally. This is kind of my area," she warned.
However mighty his performance was, it was truly lacking in some of that Kendrick magic.
And when she decided to perform Jennifer Lopez's "Booty," she had secret firepower up her sleeve.
In her most J.Lo-like jumpsuit, Kendrick showed off her pretty killer dance moves proving she can sing and dance and act. (Seriously, somebody needs to get her into the triple threat club ASAP.) But she really changed the game when she actually brought out J.Lo herself in the last few moments of her set.
"She was killing it," Lopez said, as Krasinski stood around perplexed.
"I think like John could have gotten naked and done the helicopter and it wouldn't have mattered," co-host Chrissy Teigen said. "I've decided Anna can do everything well," she added.
And the winner is...
Given her bold move, Kendrick was the clear winner for the night. The Blunt-Krasinski household remains 0 for 2.
"I mean, not surprised. John was a worthy opponent," Kendrick said of her victory.