It was an 18th straight win for the California native, fighting out of his backyard at The Forum.
"I said I was going to do it in a stylish fashion and it was done in one," McKee said.
"When I rocked him, I thought 'that's it'. After the head kick, I hit him with that uppercut and I saw him quit, he didn't need any more. But like the ref says, 'don't stop punching until I tell you to'."
McKee explained he had prayed before fight and had a vision that he would be victorious, adding: "But maybe it was the 155lb fight that I saw," opening up suggestions that the pair could meet again for Freire's lightweight crown.
That question was put to Bellator president Scott Coker after the fight and he said it was a conversation he had had with McKee and the fighter's father.
"But listen," he added, "we haven't spoken to Pitbull about it. Give the kid a little break, let him see what he wants to do, but we're going to start making some calls maybe in a week or so and see what his feeling on that is."
Elsewhere on the main card, Usman Nurmagomedov - the cousin of former UFC champion Khabib Nurmagomedov - knocked out Manny Muro in a lightweight contest.
Mads Burnell beat Emmanuel Sanchez with a unanimous decision in the co-main event, Islam Mamedov defeated Brent Primus via split decision and Goiti Yamauchi beat Chris Gonzalez.
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