"Talking to all of the doctors and going through all of the testing, we have the belief that I'll have no lingering effects and I'll be able to go out there and be who I am,'' Mahomes said after clearing the protocol.
"You have to take it day by day. That's the best thing. You can only control what you can control. For me, that was coming in every day with a positive attitude, try to make myself better, try to prepare myself as if I was going to play. Luckily enough, I haven't had any symptoms and I'm able to play.''
Mahomes worked all three days of the Chiefs' practice week, so momentum had been building for his availability against the Bills.
That's a dramatic switch from last Sunday's divisional round playoff win over the Cleveland Browns. Mahomes got up groggily after taking a big hit on a running play. The Chiefs soon announced Mahomes would not return to the game and would enter the concussion protocol, though they never said he had a concussion.
Even then, there were signs Mahomes would return to play against the Bills. As he was injured, he had the presence of mind to ask the Chiefs' trainers to leave him on the field for a few moments rather than head to the sideline immediately. He wanted to delay to give backup quarterback Chad Henne time to warm up.
Mahomes, after a quick sideline exam, ran down a set of stairs behind the Chiefs' bench and then up the tunnel to the locker room.
"There's been a bunch of testing, a bunch of different things to make sure that I'm good to go and there's no lingering effects or anything like that,'' Mahomes said. "You want to be out there but you have to go through the protocol and you have to do everything the right way. You have to look at it long-term as much as you look at it short-term.''
Mahomes before the injury was also bothered with an ailing toe, which he said is feeling better than it was against the Browns.
"Luckily enough for me, it wasn't as bad as it looked and felt that day or the day after,'' he said.
Three other key Chiefs players who have been fighting injuries also were present for the start of Friday's practice: wide receiver Sammy Watkins (calf), running back Clyde Edwards-Helaire (hip, ankle) and cornerback Bashaud Breeland (concussion, shoulder).