They had some key injuries.

They missed and extra point.

They had a rare CMC fumble.

They made a huge mistake in OT not deferring.

They had a huge momentum shift with that punt turnover.

On the other hand, KC had a rare Mahomes INT, they got a couple of really bad spots, but also only lost one of 5 fumbles.

The first series, Niners were dominant on both offense and defense. KC adjusted and warmed up. OT it was clear who was better at that point.