Instead, the rookie quarterback and the Chiefs easily marched down the field for two touchdowns in their first two drives, in coasting to a 31-13 win over the visiting Indianapolis Colts on Saturday.
Kansas City's defense did the rest, making life miserable for quarterback Andrew Luck and the normally reliable Colts offense -- which failed to pick up a first down until midway through the second quarter.
And slow starts against this version of the Chiefs is never a good idea.
"We're such a different team," said Mahomes, who passed for 278 yards and ran for a touchdown. "We have such young players. We have such confidence we're going to win every single game."
Chiefs running back Damien Williams managed 129 yards and a score on the less-than-ideal playing surface, with an early-morning snowstorm turning the grass playing surface to muck. The always-dangerous Tyreek Hill added 72 yards receiving and ran for a TD as well.
Up next for the Chiefs, who advanced to the AFC title game for the first time since 1994: The winner of Sunday's game between the Los Angeles Chargers and defending conference champion New England Patriots.
"We wanted to light up the city," Chiefs defensive tackle Chris Jones said. "We didn't want to take the road down memory lane."
Luck was limited to 203 yards passing for the Colts, who rallied from 1-5 start to finish 10-6 in the regular season and top the Houston Texans in last week's wild-card game.
But the defense had no answers for Mahomes and the Chiefs' early ability to drive down the field practically unscathed.
"Was not expecting it to end today," Colts coach Frank Reich said. "We knew we were going up against a very good team, a very well-coached team. It's hard to lose. It's hard to lose when you've come this far with the team that we have and the guys that we have, so credit to the Chiefs.
"They outcoached us, they outplayed us. We just gave them too many opportunities."