Virtually all the students have handicaps since they haven't had much sleep. To be specific:
Hiroki was stabbed in the arm and shot in the leg before fighting Kiriyama.
When you realize that Kiriyama fought in The Program while wearing a bullet proof vest that weighs him down. Mokona Zero
The vest does slow him down but it also protects him from most of the damage he took so it was a trade off which shouldn't count. In the manga Hiroki would have killed him if he hadn't had it on and his film and novel versions he would have killed by Mitsuko.
Also it should be noted, since he's an Empty Shell, he wasn't even trying.