Third downs and a stellar red zone defense
Mahomes had Kelce and the occasional pass in the flat for short completions, but to win a game with that as your offensive base, you need to win in key situations. Dinking and dunking is fine, but you have to win on third down to stay on the field and turn your red zone opportunities into touchdowns. The Chiefs were the third-best third-down team in the league during the regular season and, as I wrote about in the preview, have dominated opposing defenses in the red zone with Mahomes the past three postseasons.

Well, the Buccaneers dominated in both situations. Mahomes converted the first third down the Chiefs faced with an 11-yard scramble and then failed on eight consecutive third-down tries. The next time the Chiefs picked up a third-down conversion was with 5:43 to go in the fourth quarter, when the game was over. Unsurprisingly, pressure caused problems on third downs, as Mahomes was bothered on 61.5% of his third-down dropbacks.

If you're not hitting any deep plays and you're struggling to sustain drives, the only path to scoring is succeeding in the red zone. This was something I thought could end up deciding the game, as a Chiefs offense that had converted 80.6% of its red zone trips over the past three playoffs with Mahomes went up against a Bucs defense that held the Chiefs to zero touchdowns in three red zone trips before slowing down the record-setting Packers red zone attack two weeks ago.

The Bucs were utterly dominant in the red zone. They faced eight Mahomes dropbacks in the red zone and limited him to three completions for 8 yards while pressuring him six times. For the second time in a row, the Bucs held the Chiefs without a touchdown in three red zone trips.

They even took it to another level by limiting the Chiefs to three lone points on a Harrison Butker field goal, as they stopped the Chiefs on downs on one drive and forced a desperate Mahomes interception on the final possession of the day. The Bucs were able to simultaneously pressure Mahomes and blanket Kansas City's receivers in reduced space:

All of this added up to a catastrophic failure for what was widely seen as an unstoppable offense. The Chiefs became just the third offense in 55 years to not score a touchdown in the Super Bowl. They failed to score a touchdown for the first time with Mahomes as a starter. I don't have his high school game logs, but he didn't have any starts at Texas Tech without a touchdown, so this might have been the first game he has ever completed without getting into the end zone at least once.

This was an old-school slap in the face for the league's most modern offense. The Chiefs could not control the line of scrimmage and, for the first time, Mahomes wasn't able to find a way to bail them out.

Bill Barnwell, ESPN.com, published 8 February 2021