Kansas City, Mo. ? The Chiefs won their first nine games a year ago, streaking toward the playoffs under new coach Andy Reid.

They were the darlings of the NFL, its biggest surprise. Then they stumbled down the stretch and were beaten in the wild-card round by the Colts.

Now, everything is reversed.

After losing its first two games, including a one-sided rout at the hands of the hapless Titans, Kansas City is riding a wave of success. Reid and Co. have won four straight and six of their past seven, putting the pressure on the Broncos in the AFC West.

They head into Sunday’s matchup with the defending Super Bowl champion Seahawks at Arrowhead Stadium as one of the NFL’s hottest teams. Now, the big question is whether they can sustain that momentum deep into the season.

Can they not only qualify for the playoffs but actually win a playoff game, something they haven’t done in more than two decades?

Good luck getting anybody in the locker room to bite on that question. But in conversations throughout the week, players did reveal the recipe for their dramatic turnaround.

Playing defense: Simple, right? Stop the opponent from scoring to win games. But such a simple concept is much more difficult in practice, especially in a league that has been tailored to produce big yardage and high scores. Yet the Chiefs have only allowed more than 20 points once since their 0-2 start, and that was in a 22-17 loss in San Francisco.

“I think we probably have a better understanding of the defense than maybe we had last year,” Reid said. “They’re playing well together, as a unit, a team.”

That’s been critical given the number of injuries the defense has sustained.

Defensive tackle Mike DeVito and linebacker Derrick Johnson went down with season-ending injuries in Week 1, and safety Eric Berry has missed most of the first half of the season. But a group of unheralded backups, including leading tackler Josh Mauga, have filled in admirably.

The result has been the league’s best pass defense, allowing just 205.3 yards per game.

“Just playing together, being consistent, being all on the same page,” Mauga said, “and then our preparation. Guys around here are doing a great job, coaches included on helping us understand formations and what they’re trying to do to us. It allows us to play fast.”

Executing under pressure: The Chiefs are third in the league in third-down conversions, picking up a first down nearly 50 percent of the time. They’re also fourth in the league in red-zone touchdown rate, putting up seven points on 69 percent of trips.

Those are the kind of under-the-radar stats that help win games.

“A reason is our balance this year,” Chiefs quarterback Alex Smith said.