The ferocious finish of the UFC on FOX 6 bout came at 2:32 of the second round.
The two fought an evenly contested first round, but Lamas seized momentum early in the second taking top position off a scramble. Working from inside Koch's guard, he cut his opponent open with an elbow, and then continued that beating with a series of power shots from the top that forced referee John McCarthy to step in.
It was a performance worthy of his "Bully" nickname.
"If i get on top of you, you better watch out," he said. "I'm not letting you up until you're bloody or you're knocked out."
Lamas is a perfect 4-0 since making the move to 145 pounds. Three of those wins are by finish, including one over fellow contender Cub Swanson. He's now 13-2 overall.
Koch, once considered the No. 1 contender in the division, fell to 13-2. He was fighting for the first time in 16 months after an injury and subsequent rehabilitation.