The fight went the five-round distance, with the judges scoring it 49-46 49-46 49-46 in favour of Rockhold.
Former US Army Special Forces soldier Kennedy looked to grapple his way to a win, but was pummelled by Rockhold in the stand-up with Kennedy kicking more than he punched.
"I could've let a couple combinations go," Rockhold said. "He does some funky stuff. It's hard to let things go when you know he's going to shoot.
"It (defending against takedowns) was one of the main focuses of my [training] camp. He's a great wrestler, so tenacious. What he lacks in technique, he makes up for in desire.
"I knew I couldn't get stale."
Rockhold's record is now 10-1, while Kennedy's stands at 14-4.