Kansas City, Mo. — The Kansas City Chiefs built a defense and signed a backup quarterback that were good enough to preserve a win.

Now, are they good enough to win on their own?

The Chiefs, who lost Patrick Mahomes to a concussion in the third quarter of Sunday's divisional-round win over Cleveland, might have to find out with their hopes of back-to-back AFC titles and a Super Bowl repeat on the line.

Mahomes remained in the league's concussion protocol Monday and coach Andy Reid declined to speculate on when he'll be cleared.

“Because of the protocol it's a no-brainer,” Reid explained of the decision, which rests not in his hands but those of team doctors and outside experts. “You don’t even have to think about it. You just go forward. You have an answer if he's there and if he's not there. I can't tell you an answer from a medical standpoint. I just don't know.”

If Mahomes is unable to play, 35-year-old journeyman Chad Henne would start against Buffalo in Sunday's AFC title game.

Henne took over when Mahomes sustained the concussion with the Chiefs leading 19-10, and he finished the drive by leading Kansas City to a field goal. But more memorable will be the two plays he made in the fourth quarter, when the Chiefs were trying to hold onto a 22-17 lead and run out the clock on the win.

On third-and-14 in his own territory, Henne scrambled to his left and found some open space, then sacrificed his body by diving for the first-down marker. Henne came up just short, and when Reid elected to go for it rather than punt, the coach put the game in his hands by calling a short pass play to Tyreek Hill that gave Kansas City a first down.

“I thought Chad played with great composure, particularly for that situation,” Reid said, “and to come down to that last series, that big run was gravy. He dusted off those old legs, got them moving a bit, came up a hair short, came back and made a nice throw to Tyreek to clinch it.”

That throw wouldn't have been possible without a big stand by the Kansas City defense.

After allowing the Browns to convert their own fourth down with 5:30 to go, they stuffed Nick Chubb and forced Baker Mayfield to throw an incompletion. And when they tackled Kareem Hunt for a loss on the ensuing third-down pass play, the Browns were forced to punt with 4:23 left in the game.

They never got another chance with the ball.

“They have trust in each other to get that done,” Reid said. “I'd rather not have it have to be that way, bigger leads, but the bottom line is you attempt to win the football game, and you do it the best way you can against the best competition in this league. At times you have to reach down, reach a little deeper, and really, whatever the term is, to get in there and use that intestinal fortitude to get you over the hump.”

The pass game kept humming even when Mahomes left the game. Henne was 6 of 8 for 66 yards, though he did make a poor decision on an interception in the end zone. It helps to have tight end Travis Kelce (eight catches, 109 yards and a TD) and Tyreek Hill (eight catches, 110 yards and the game's most important first down) helping him out.

Notes: Mahomes wasn't the only player to sustain a concussion Sunday. Top cornerback Bashaud Breeland left the game in the second half, and with backup Rashad Fenton out with an ankle injury, the Chiefs' depth is limited in the defensive backfield. ... Reid moved into a tie with Chuck Noll for the fifth-most postseason wins (16) by a coach in NFL history. Two more wins would move him past Joe Gibbs for fourth place, leaving only Bill Belichick, Tom Landry and Don Shula ahead of him. ... The Chiefs have Tuesday off before returning to practice Wednesday, at which point they hope to have a clearer picture of whether Mahomes will be available against Buffalo on Sunday.