The Kansas City Chiefs fell to the Tennessee Titans by a score of 22-21 Saturday afternoon at Arrowhead Stadium in the Wild Card round of the AFC playoffs.

The Titans scored 19 unanswered points in the second half, which erased a 21-3 first-half deficit and helped them get the comeback victory.

Here are six observations from Saturday:

1. The phrase "forward progress" will forever remind fans of this game

There were multiple situations throughout the game on Saturday that the Chiefs had an opportunity to put the game away, but much of what's going to be discussed regarding this game were a couple of "forward progress" calls that took some points off the board for the Chiefs.

The first was on a sack by veteran linebacker Derrick Johnson, who knifed through the middle of the Titans' offensive line and put a huge hit on Mariota, who fumbled the ball before he hit the ground. The ball was recovered by the Chiefs but the call was that forward progress had stopped when Mariota was hit. The play was blown dead and wasn't challengeable by the Chiefs.

Then, later in the game on a two-point conversion attempt by the Titans, quarterback Marcus Mariota was spun around and sacked as he tried to escape the grasp of Chiefs' safety Daniel Sorensen, who forced the ball out before Mariota hit the ground and it was picked up and returned the other way for two points by the Chiefs, which would have actually given them a 23-22 lead late in the game.

But again, the call was that Mariota's forward progress had been stopped.

2. The Chiefs started out hot

Less than 15 minutes into the game, the Chiefs raced out to a 14-0 lead after two quick scoring drives on their first three attempts.

Chiefs' quarterback Alex Smith was 8 of 11 for 154 yards and a touchdown in the first quarter, finding tight end Travis Kelce for a 13-yard touchdown late in the opening quarter.

Chiefs' rookie running back Kareem Hunt got the Chiefs on the board with a 1-yard touchdown on the previous drive, which was highlighted by a couple of chunk plays on throws from Smith to Tyreek Hill (45 yards) and Kelce (27 yards).

The Chiefs' offensive line did a great job early in the game of giving Smith time in the pocket and survey the field.

After the Chiefs' third offensive drive, which resulted in Kelce's touchdown, they were averaging 10.5 yards per play, and had converted two of three third downs and both trips to the red zone.

3. Marcus Peters added to his NFL-leading interception total

There's not a player who has more interceptions since the beginning of the 2015 season than the Chiefs' Marcus Peters, who added the 21st pick of his career midway through the second quarter.

Peters, who had his eyes in the backfield off the snap, read the play the whole way and came off his man to make the play.

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4. Derrick Johnson's hit on Mariota, unreal

Veteran linebacker Derrick Johnson, who is already the Chiefs' leading tackler and one of the best defensive players in franchise history, had one of the biggest hits of his career on his sack of Mariota that was one of the "forward progress" plays.

What shouldn't be lost on that play is the hit Johnson put on Mariota, who was basically speared the ground after Johnson came on the delayed blitz.

5. Kelce leaves late game in first half, Chris Jones also injures knee

Late in the first half with the Chiefs running the two-minute drill, Kelce caught a short pass to the left for a gain of 12 yards but took a big helmet-to-helmet hit after he raced up field for a few additional yards. He was taken off the field and later ruled out of the game with a concussion.

Kelce finished with four receptions for 66 yards and a touchdown.

The Chiefs' offense finished that particular drive strong, with second-year receiver Demarcus Robinson stepping up and making a few plays.

Robinson had four catches for 56 yards on the drive, including the 14-yard touchdown that came on a hurry-up play with less than 10 seconds remaining in the first half.

With Kelce sidelined in the second half, the Chiefs managed just 61 yards of total offense.

Defensive lineman Chris Jones also left the game in the third quarter with a knee injury and he did not return.

6. Titans grab three second-half touchdowns, including one Mariota threw to himself

Midway through the third quarter, the Chiefs' defense faced a third-and-goal from the six-yard line.

Mariota, who had just been sacked on the previous play as Justin Houston chased him out of bounds, rolled to his left on the third-down play and attempted to a throw to a receiver in the end zone but the ball was deflected by Chiefs' cornerback Darrelle Revis, and it right back into the hands of Mariota, who caught it and dove for the pylon for a touchdown.

The play brought the game to 21-10 with 6:44 left in the third quarter.

It was the first time a quarterback has thrown a touchdown to himself since Brad Johnson did that with the Minnesota Vikings in 1997.

The touchdown was also one of the seven third-down conversions for the Titans in the second half, which came on just seven attempts. Outside of a kneel down to finish the game, the Titans' offense was a perfect 7 of 7 on third down in the second half.

Soon after that Mariota touchdown thrown to himself, the Chiefs had a chance to add to their lead after Titans' rookie returner Adoree' Jackson muffed a punt, which gave the Chiefs fantastic field position at the 28-yard line, but the drive ultimately lost three yards and Harrison Butker's 48-yard field goal hit the left upright and was no good.

Then, after Titans' running back Derrick Henry raced 22 yards for a touchdown on the second play of the fourth quarter, which brought the game to within a possession at 21-16, the Titans were setup for a go-ahead scoring opportunity after Smith's third-down pass was dropped by tight end Orson Charles. It gave the Titans the ball back with 11:15 remaining in the game.

After three third-down conversions extended their drive, Mariota ultimately hit veteran receiver Eric Decker for a 22-yard touchdown on second-and-10 with 6:10 left in the game. That led to the other "forward progress" call on the two-point attempt, which could have given the Chiefs a lead and the ball late in the game.