"The Tonight Show With Jimmy Fallon" and its popular segment, a lip-sync battle, brought two actual singers to the stage along with show host in what has been labeled as an epic battle.

Gwen Stefani and Blake Shelton, singers and coaches of the show The Voice, were the two guests on the show, CNN reported.

Despite Stefani forgetting which show she was on and calling the host by his former TV personality "Jimmy Kimmel," the ensuing battle between the three has been labeled epic.

The rules are simple with each guest and Fallon taking turns lip-synching songs of their choice.

Shelton kicked off round one by performing "Puttin on the Ritz" by Tacos, followed by Fallon's "Burn" by Ellie Goulding, and Stefani wrapping up with Carly Rae Jepsen's 2011 hit "Call Me Maybe," Today reported.

The next round began with Shelton singing "Nothing's Gonna Stop Us Now" by Starship, and Fallon followed with "Cocktails for Two" by Spike Jones.

Each performance was on par with the others, until Stefani and Shelton whipped out a duet that made the whole segment memorable.

They sang "Endless Love." Stefani did the Lionel Richie part, and Shelton subbed for Diana Ross, CNN reported.

"That's it, that's it. Game over, contest over. Blake Shelton and Gwen Stefani win," Fallon said at the end of the duet, screaming over the applause from the audience as the two singers calmly smiled and took a bow.

Stefani is the latest to join The Voice judges panel, which includes all male judges otherwise such as Shelton, Pharrell Williams and Adam Levine.

The new season of the show begins Sept. 22, and all the guys gushed about Stefani to Us Magazine.

Shelton said, "Gwen Stefani is an icon."

The lead singer of band No Doubt, which formed in the late 1980s and came out with a hit in the early 1990s, "Don't Speak," praised Williams.

She said he had changed everything for her band.

"The level of brilliance Gwen and Pharrell brought into the game. ... I absolutely did not see this coming," Shelton said.