The Brit was desperate to take the fight to the ground, most notably by trying to pull guard. Johnson, knowing full well that's what Sass wanted, did a mostly admirable defending until he didn't finish an escape. With one foot left in and unable to roll through to defend, Sass secured the heel hook.
It's a nice win for Sass, but so long as the guard is where fights have to take place in order for him to win, his upside is extremely limited.
Here's our live blog of the fight:
Round 1 Flying knee attempt by Sass. Sass shoots on Johnson off another. Johnson fights him off. Sass shoots in and tries to pull guard but Johnson backs away. Sass lands a straight right. Johnson drops Sass with a punch and a knee. Sass is in trouble. He recovers. Sass stumbles in and quickly tries to pull guard. Johnson tees off before backing away. Sass misses with a spinning elbow attack. Sass drops to guard. Sass goes after a leg. Sass going after a heel hook. Johnson surviving. Sass finishes it and gets the submission.