Kansas City, Mo. ? Before Scott Pioli and Todd Haley arrived, most Chiefs fans had written off Dwayne Bowe a coach killer, Glenn Dorsey as a first-round bust and Tamba Hali as merely average.

Kansas City Chiefs coach Todd Haley watches a replay during the second half of an NFL football game against the Tennessee Titans at Arrowhead Stadium in Kansas City, Mo., Sunday, Dec. 26, 2010. The Chiefs defeated the Titans 34-14.

Derrick Johnson was supposed to be another in former general manager Carl Peterson’s long line of first-round flops. Jamaal Charles? A fumble-prone running back Peterson drafted in the middle rounds to caddy for Larry Johnson.

What nobody realized was those players and others would blossom into key ingredients in a breathtaking worst-to-first turnaround that’s produced an AFC West championship just two years after Kansas City stumbled to a 2-14 finish.

General manager Pioli and head coach Haley are deservedly drawing praise for taking the Chiefs from 10 wins in three years to 10 wins in 16 weeks. But they do not deny they were blessed with a core of talented young players when they got to Kansas City.

“The first thing you have to do when you come into a new situation is you have to be right on who the guys are that you keep around, that you think have a chance to be a part of what you’re trying to do,” Haley said Monday. “We had to make some tough decisions. At least it looks like we were right on a lot of those decisions.”

The holdovers certainly did not bring about the turnaround all by themselves. The Chiefs’ MVP without question is quarterback Matt Cassel. He was acquired along with linebacker Mike Vrabel in a trade with New England, Pioli’s first major personnel move.

In addition, rookie safety Eric Berry has solidified what had been a suspect secondary and first-year coordinators Charlie Weis and Romeo Crennel have given Haley one of the league’s most experienced, successful staffs.

“It’s hard to put into words how big their impact has been,” Haley has said.

But the foundation for Kansas City’s first division championship in seven years was already in place when the Pioli-Haley team hit town.

It’s just that nobody realized it.

So what’s made the difference? Was it the natural process of maturing? Improved leadership and coaching?

“A little bit of both,” Haley said. “To be a successful team year in and year out, you have to develop your second-, third- and fourth-year players, and even fifth-year players. The way you do that is with coaching. To be successful you need good players and good coaching. You can’t just do it with one or the other. You just can’t.”

Peterson might still be general manager and Herm Edwards might still be coach if not for a boneheaded flub that Bowe made against San Diego on Dec. 14, 2008. The first-round pick out of LSU was on the “hands” team, positioned to get the ball when the Chargers made an onside kick in the final minute. The ball bounced off his chest and the Chargers recovered, then scored a quick touchdown for a stunning 22-21 victory.

Team owner Clark Hunt, his head buried in his hands, looked sick. The next day, Peterson resigned. A few weeks later, Pioli fired Herm Edwards and hired Haley off the Arizona Cardinals staff.

Now, though still inconsistent, Bowe has become one of the most dangerous wide receivers in the country. He set a team record this year with touchdown catches in seven straight games and had a 75-yard catch-and-run for a TD on Sunday against Tennessee, giving him a franchise-record 15 touchdowns for the year.

Charles is an even bigger success story. Since he was given a chance to start when Pioli and Haley released the trouble-making Johnson last year, Charles has been spectacular. He caught two touchdown passes on Sunday and boosted his season rushing total to 1,380 yards. He’s averaging about 6 yards a carry — not far from Jim Brown’s NFL record.

When he came out of Texas as a junior, however, he probably had more maturing to do than most players.

“It’s easy to say he’s a great player and he was here,” Haley said. “But Jamaal, he has developed. It’s really an unbelievable development you’ve seen in him and you’ve got to give everybody credit.”

Hali, moved from defensive end to linebacker, leads the Chiefs with 11 sacks. Dorsey has become a solid defensive lineman.

Johnson, a linebacker drafted in the first round in 2005, spent much of Haley’s first season in the doghouse. This year he’s exploded into the player the Chiefs always projected and was named AFC defensive player of the week when ringing up 17 tackles against St. Louis.

“They’re all a bunch of guys who are developing each and every day,” Haley said. “You can see that. The coaches have done a terrific job last year and this year of helping in that process and the players themselves have done a terrific job. It feels good as the head coach to see some of these guys grow up before your eyes and become players before your eyes.”