Mariota fired a 22-yard touchdown pass to Eric Decker with 6:06 remaining for the last of 19 consecutive points the Titans scored in the second half.
The Chiefs, who earned an opportunity to host a postseason game by repeating as AFC West champions, lost their sixth straight home playoff game, a streak that dates to 1994 when Joe Montana quarterbacked Kansas City.
The Titans converted three third downs on their game-winning drive, including a 17-yard keeper by Mariota on a play which also included a holding penalty against the Chiefs.
Mariota finished 19 of 31 for 205 yards passing and two touchdowns. Derrick Henry added 156 yards rushing on 23 carries, including a 35-yard touchdown burst with 14:08 remaining.
"Executing better. That's what I think it comes down to, guys just making plays. It helps if you can run the football. I thought Derrick had a great game for us and things just clicked,'' Mariota said of the Titans' rally
Said Henry, "It's been a long time coming for this team to get to the playoffs and get a win. We came into a hostile environment against a great team and a good defense. We stuck together. We got down early, came in at halftime and we just believed in each other.''
Tennessee, which advanced to the playoffs with a 9-7 record, failed on a pair of two-point conversions after the fourth-quarter touchdowns. On the second, Mariota appeared to lose a fumble, which the Chiefs returned for a two-point conversion only to have the play ruled dead.
For Tennessee coach Mike Mularkey, whose job was rumored to be on the line should the Titans lose, it was a relief.
"I don't think (the discussion) is fair to my family. If it has an effect on my family, it has an effect on me. So yeah, it had a big effect on me. I didn't have any support to say I was (secure). I just assumed the worst,'' Mularkey said.
But his team made sure that talk would quiet down.
"It's this team. They have each other's backs and they always have.''
The Chiefs struck for touchdowns on two first-quarter possessions. Kareem Hunt scored on a 1-yard plunge to cap an 81-yard march. Tight end Travis Kelce added a 13-yard reception from Alex Smith to complete a 76-yard march.
Those drives helped boost Smith's passing total to 154 yards for the quarter as he completed 8 of 11 attempts, including back-to-back throws of 45 and 27 yards to Tyreek Hill and Kelce on the first TD march.
Kansas City executed its two-minute drill to perfection to end the half, starting from its 21 with 1:48 left before Smith connected with Demarcus Robinson for a 14-yard touchdown with three seconds remaining. Robinson had four catches on the drive as Smith passed for 231 first-half yards, going 19-of-23.
The Titans' only first-half score came on a 49-yard field goal by Ryan Succop with two minutes left. A vicious sack of Mariota by Chiefs linebacker Derrick Johnson caused the drive to stall. Although Mariota fumbled on the play, he was ruled down by forward contact and a review the Chiefs wanted was not allowed.
"I don't know how you can call a guy down or blow the whistle when he hadn't hit the ground yet, especially on a sack,'' Johnson said.
Smith added just 33 yards passing in the second half. The Chiefs' best opportunity for a second-half score was a 48-yard field goal attempt by Harrison Butker that missed off the left upright with 2:25 left in the third quarter.
The Chiefs' QB was still trying to process blowing a 21-3 lead afterward.
"We had a chance and now it's gone, it's over. ... It's definitely a shock. Definitely didn't feel like we played like we were capable. Certainly disappointing.''
--Field Level Media
Tennessee | Kansas City | |
Derrick Henry | Player | Kareem Hunt |
23 | Attempts | 11 |
156 | Yards | 42 |
6.8 | Avg Yards | 3.8 |
1 | Touchdowns | 1 |
35 | Long | 16 |
Tennessee | Kansas City | |
Delanie Walker | Player | Tyreek Hill |
6 | Receptions | 7 |
74 | Yards | 87 |
12.3 | Avg Yards | 12.4 |
0 | Touchdowns | 0 |
22 | Long | 45 |
Yards | Scoring | Defense | ||||||
Team | Tot | Rus | Pas | TD | FG | INT | Sck | FF |
Tennessee | 397 | 202 | 195 | 3 | 1 | 0 | 4.0 | 0 |
Kansas City | 325 | 69 | 256 | 3 | 0 | 1 | 2.0 | 1 |