Patrick Mahomes passed for 404 yards and five touchdowns Sunday as the Kansas City Chiefs began their bid for a third straight conference title by downing the visiting Pittsburgh Steelers 42-21 in the AFC wild-card round.

The loss likely will be the last NFL game for the Steelers' Ben Roethlisberger, who is expected to announce his retirement. The 39-year-old quarterback started slowly before finishing with 215 yards passing, going 29 of 44 with two touchdowns.

Kansas City, seeded No. 2 after winning nine of its last 10 regular-season games, will play at home again next Sunday in the divisional round, hosting the Buffalo Bills. Buffalo won at Kansas City 38-20 in Week 5.

The Chiefs scored touchdowns on six straight possessions bridging the two halves. A 1-yard lob to tackle-eligible Nick Allegretti and a 31-yard strike to Tyreek Hill boosted the lead to 35-7 before six minutes had elapsed in the second half.

Mahomes, who was intercepted once, went 30 of 39 on the night and reached 400 yards passing before the end of third period.

Jerick McKinnon, who has battled injuries and played sparingly, had 18 touches for 142 yards and a TD reception. Travis Kelce gained 108 yards on five catches and threw a short TD pass, one of two caught by Byron Pringle.

The seventh-seeded Steelers did not crack Kansas City territory until the second half when Roethlisberger connected for scores to Diontae Johnson and James Washington.

The Chiefs gained 302 first-half yards and Mahomes fired three touchdowns, all in the second quarter, including a 45-yarder to Kelce with 13 seconds remaining for a 21-7 halftime margin.

McKinnon and Pringle caught first-half TDs of 4 and 12 yards, though the Chiefs had trouble getting untracked. On their first five possessions, they punted three times, Mahomes threw an interception and Darrel Williams lost a fumble.

T.J. Watt returned the fumble 24 yards to provide a 7-0 lead for the Steelers with 10:41 left in the half. However, Pittsburgh finished the half with just 45 yards, two first downs and punts on each of its seven series.