Chuck Liddell already has his fight strategy for his 3rd scrap with Tito Ortiz -- "I'm gonna knock his head off."
TMZ Sports broke the story ... the 48-year-old MMA legend is coming out of retirement to fight on a MMA card promoted by Oscar De La Hoya -- and can't wait to get back in the cage with his old rival.
"When it's all over with, it's gonna be 3-0," Liddell said ... bragging about the 2 wins he already racked up over Ortiz during their fights back in the mid-2000s.