Johnson of the American Top Team used his size, strength and wrestling to overwhelm Tony Lopez through five rounds to capture the heavyweight belt.
Johnson took down Lopez with ease and forced his experienced opponent to reside on his back for the majority of the fight. Although Lopez tried to put together some offense with armbars, Johnson's top game proved too powerful.
"My bread and butter is wrestling and you got to stick with what you know," Johnson said.
Lopez, who entered the fight as both the promotion's heavyweight and light heavyweight belt, not only dropped the belt but also a 16-fight win streak.
In a fight for the vacant welterweight belt, Mulhern went after Koffi Adzitso with submission after submission until finally forcing the tapout with a rear-naked choke at one minute and 36 seconds of the second round.
Mulhern, who won at the previous King of the Cage installment on HDNet against Rich Clementi, improved to 11-1 with the title win.
Mike Kyle def. Jon Murphy via TKO - Round 2, 4:53
Dustin Akbari def. Jack Montgomery via KO - Round 1, 2:30
Tony Johnson def. Tony Lopez via unanimous decison after five rounds
Jaime Jara def. Tim Means via submission (guillotine choke) - Round 1, 2:19
Nick Gaston def. Mike Guidry via submission (keylock) - Round 1, 4:49
Quinn Mulhern def. Koffi Adzitso via submission (rear-naked choke) - Round 2, 1:36