Bill Walsh, the great 49ers coach said that the key to winning is to have a late game pass rush. I always thought that was an interesting comment from a coach who was a offensive genius, but he is right.
The San Francisco pass rush had Mahommes looking quite mortal most of the game. Then in the last 7 minutes of the game, when they needed the pass rush the most, it disappeared. Don't know if KC finally figured out how to slow them down or they ran out of gas, but Mahommes finally looked comfortable in the pocket and KC dropped the hammer.
Conversely, the KC pass rush came alive during this period too, and Garrappolo was under very intense pressure. San Francisco could not sustain any drives to score or at least take chunks of time off of the clock. That was the game right there.