With reporting by James Lacsina

When Busta Rhymes asked Eminem to co-star on his new single "Calm Down," the Dungeon Dragon got a little more than he bargained for. What started as a simple three-minute song, with a few verses and a hook, turned into a nearly six-minute rap throw down.

"Originally, the song was like three minutes and eight seconds. I had two 16-bar verses on it and the hook that's there," Busta explained to MTV News on Wednesday.

Busta sent the song to Em, expecting to get a standard 16-bar rhyme, but Slim Shady sent him a performance more than three times the usual length. "Eminem's verse comes on and it's like 42 bars," Busta said.

The length and intensity of Em's verse made Busta a bit uncomfortable. Though the two came to the Scoop DeVille-produced track as collaborators, Bus acknowledges that there was a "respectful competition" between them.

"You're not just gonna mop the floor with me on my record," Bus remembers thinking to himself. "I didn't expect any less because that's what Em does, but that's what people know Busta Rhymes for doing."

Busta says he went back to write a longer verse to match Em's rhymes and that's where "Calm Down" began to turn into an anything-you-can-do-I-can-do-better affair. After that, the two decided that Eminem would mix the record in his Detroit studio, but after traveling to the D, the maniacal MC and music producer called an audible.

"I'm in there, Em hears the verse. He's vibing for like two or three hours... He said, 'We not mixing today.' Em was like, 'Yo man. My energy don't match your energy right now,'" he remembered. "I'm listening to the verse like, 'You f--kin' spazzed out already. What more spazzing out do you wanna do?'"

Bus returned to New York, and a little over a month passed before Em volleyed his final verse back and, of course, Busta had to have the last word. "Em sends back his verse again. So now he's at 62 bars and I'm like, 'F--k that, I'm going back again,'" he said.

Eventually, the two called it quits and decided to put the song out before things got truly out of hand. The end result is a thumping growl of rap aggression and complex lyricism -- one that Busta is proud of. "It turned from a song to a piece of art," Busta concluded. "Just a fundamental hip-hop record."