Mariota spread the ball around to eight receivers - including himself - and deftly avoided Kansas City's pass rush, aside from two sacks.
Midway through the fourth quarter, after the Titans took their first lead of the game, they attempted a two-point conversion.
Kelce was knocked out of the game in the second period with a concussion, following an ugly head-to-head collision with a Tennessee defender.
The team is led by rookie running back Kareem Hunt who led the league in rushing (1,327 yards).
If he's not serving as offensive coordinator for the New England Patriots next season, most people assume Josh McDaniels will be coaching either the New York Giants, the Chicago Bears or the Indianapolis Colts.
The Chiefs needed a break, and seemed to get it when Peters stripped the ball from Henry; Johnson recovered the ball and ran it back 56 yards. But the Titans mounted a comeback, and former Chiefs kicker Ryan Succop hit a 52-yard field goal on the final play of the game - after a timeout by Andy Reid gave him another shot - to give Tennessee the win.
Fans unfurled a field-length flag during the rendition, and a B-2 bomber flew overhead, while the Titans and the rest of the Chiefs stood on their respective sidelines at attention.
Kansas City (10-6) is heavily favored heading into the game thanks to the Arrowhead advantage and its recent four-game winning streak.
96 percent of selected analysts are picking the Chiefs to win per NFL Pick Watch.
Chiefs president Mark Donovan vowed that their game against the Titans would sell out, but there were still plenty of seats available late in the week. For the second time in the game, referee Jeff Triplette promptly waved off a potentially game-changing play in the Chiefs' favor by saying Mariota was down before the fumble due to forward progress.
The fourth-seeded Chiefs won four straight games to cap the regular season and capture their second straight AFC West title.
In National Football Conference action later Saturday, the Los Angeles Rams hosted the Atlanta Falcons.