Charlie Riedel/Associated Press

If Saturday's contest was Alex Smith's last game at Arrowhead Stadium, it won't be remembered fondly. 

While Smith—who reportedly could be traded in the offseason—helped lead the Kansas City Chiefs to a 21-3 halftime edge, the Tennessee Titans erased that deficit and scored 19 unanswered points in the second half to pull off a 22-21 AFC Wild Card stunner for their first postseason win since January 2004. 

Quarterback Marcus Mariota led the late surge, and his 22-yard touchdown strike down the seam to Eric Decker with 6:06 remaining in regulation capped off Tennessee's improbable comeback. 

According to ESPN Stats & Info, the Titans joined the Buffalo Bills (1992), Indianapolis Colts (2013) and New England Patriots (Super Bowl 51) as the only teams to erase an 18-point halftime playoff deficit in the Super Bowl era. 

Tennessee's second-half awakening was the product of several factors, the biggest of which was Mariota's brilliant playmaking with his arm and legs. 

Although the Titans didn't muster a touchdown over the first 30 minutes, Mariota—who completed 19 of 31 passes for 205 yards—marched his troops 91 yards on the first drive of the second half to make a statement. 

The tide-turning possession, which spanned 15 plays and lasted 8:29, culminated with a Mariota touchdown pass to himself after Darrelle Revis batted the ball back into the quarterback's arms. He ran it into the end zone for one of the most bizarre scores in playoff history: 

The Titans also leaned heavily on running back Derrick Henry, who rushed 23 times for 156 yards, including a 35-yard jaunt to paydirt 52 seconds into the fourth quarter: 

Henry later gave Tennessee a scare when he appeared to cough up the ball on a play that resulted in a Kansas City scoop-and-score with 2:00 to go, but the 2015 Heisman Trophy winner was ruled down upon review. 

Mariota tacked on 46 rushing yards, and his ability to extend drives throughout the second half proved crucial against a Chiefs defense that seemingly couldn't get off the field. He also came up with a clutch block to spring Henry for a 22-yard gain on 3rd-and-10 on the Titans' final drive

The other issue for Kansas City was its offense flatlined after going up 18. 

While Smith (264 yards, two touchdowns) was firing on all cylinders early, the play-calling became vanilla and consisted of more east-west concepts than north-south ones that could have pressured Tennessee's secondary. 

Of course, it didn't help that tight end Travis Kelce was ruled out with a concussion after he took a shot to the head in the second quarter. 

As a result of those issues, combined with some untimely drops, the Titans were able to post a near-five minute edge in time of possession and send the Chiefs into an exclusively futile club, according to ESPN Stats & Info's Micah Adams: 

Now headed for an offseason full of question marks, the Chiefs will have to evaluate whether Smith will be the man to lead the charge in 2018 or if first-round pick Patrick Mahomes is ready to take the reins. 

Right tackle Mitchell Schwartz offered a glowing review of Smith after the loss, via NFL Network's James Palmer: 

The Titans, meanwhile, await a second-round playoff game against either the New England Patriots or Pittsburgh Steelers. Tennessee will meet the Patriots if the Jacksonville Jaguars win on Sunday, but a win by the sixth-seeded Bills would send the Titans to Heinz Field next weekend. 

Beyond securing a spot in the divisional round, the Titans may have saved head coach Mike Mularkey's job with the win after NFL Network's Ian Rapoport reported the front office was preparing to move on if the team lost.