PITTSBURGH — The Pittsburgh Steelers spent two years rebuilding themselves on the fly, a necessary process that frequently looked more erratic than inspiring.

Consider the project nearly complete. The surging Steelers are heading to the playoffs.

Ben Roethlisberger passed for 220 yards and a touchdown, Le’Veon Bell added a score and the Steelers locked up a postseason berth with a methodical 20-12 win over the Kansas City Chiefs on Sunday.

“It was such a sense of urgency this week, knowing what was at stake,” defensive end Cam Heyward said. “I just thought we answered the challenge.”

Pittsburgh (10-5) faces Cincinnati next Sunday night for the AFC North title. Either way, the Steelers are in the playoffs for the first time since Tim Tebow and Denver stunned the defending AFC champions in the wild-card round three years ago.

That group was on the tail end of a stretch that saw Pittsburgh put together three Super Bowl appearances in six years. This group is decidedly younger. The Steelers won their third straight and are 7-2 since an October loss at Cleveland left them at 3-3.

Those days suddenly seem long ago. Pittsburgh kept the Chiefs in check behind a resurgent pass rush energized by the return of James Harrison. The 36-year-old linebacker missed last week’s win over Atlanta because of a knee problem. He returned to pick up 1.5 of Pittsburgh’s season-high six sacks.

“We’re headed in the right direction,” Harrison said.

The Chiefs? Not so much. Alex Smith passed for a season-high 311 yards, but Kansas City lost for the fourth time in five games. The Chiefs need to beat San Diego next week and get some help to make it back to the playoffs for a second straight year under Coach Andy Reid.

Moving the ball wasn’t a problem. The Chiefs outgained the NFL’s top-ranked offense 327-288 but couldn’t seem to get the one momentum-turning play that mattered. Kansas City had six drives into Pittsburgh territory end with four field goals by Cairo Santos, a Jamaal Charles fumble, and a fourth-down gamble late in the first half that fizzled.

“There are so many little things that happened,” Smith said. “They’re not big things, but just little stuff that gets magnified.”

That’s the case this time of year. And the Steelers, after a brief foray into 8-8 mediocrity in 2012 and 2013, are back playing their best football when the temperature drops. A roster that’s undergone a youth movement since a Super Bowl loss to Green Bay four years ago is growing up quickly, though with a few familiar faces leading the way.

Roethlisberger wasn’t as dynamic as he’s been at times this season but led a pair of long touchdown drives. The second ended with a 3-yard strike to Antonio Brown that gave Pittsburgh a 17-6 lead late in the third quarter. Roethlisberger briefly went to the locker room because of a right knee injury but returned to guide a 12-play, 70-yard march that ended with Shaun Suisham’s 23-yard field goal that made it 20-12 with 4:04 remaining.

A team that struggled closing out opponents early in the year has won three straight, featuring a dominant finishing kick.

“You can see us cutting down the mistakes,” Bell said.