Kansas City, Mo. ? Kansas City Chiefs coach Todd Haley preached about “The Plan” all through training camp, referring to the unusual approach he took after a most unusual offseason.

Rather than hit the ground running like most teams did after the lockout, Haley took a more deliberate pace in practice. He played his starters sparingly in early preseason games, slowly trying to build toward the regular season opener against Buffalo.

Well, “The Plan” sure appeared to flop on Sunday.

Ryan Fitzpatrick threw four touchdown passes, two of them to journeyman tight end Scott Chandler, and the Bills romped to a 41-7 victory at Arrowhead Stadium. It was the most lopsided season-opening loss in franchise history, and the Chiefs’ worst home defeat since a 45-0 loss to the Pittsburgh Steelers 35 years ago.

“I’m taking 100 percent responsibility for our team not being ready to go,” Haley said. “You can point the finger right at Todd Haley. I’m taking responsibility.”

Not that there wasn’t plenty to go around.

Dexter McCluster fumbled the opening kickoff and the Bills turned it into a touchdown. Jamaal Charles fumbled later in the game to set up a field goal.

Matt Cassel was dropped for a sack after a video review by the officiating crew wiped away a would-be touchdown pass to Leonard Pope, and the lost yardage forced Ryan Succop to try a 49-yard field goal that he pushed wide right.

“We didn’t execute today,” Charles said, “and that’s on us.”

Cassel threw for 119 yards with a touchdown and an interception, while Charles was held to 56 yards rushing by a defense that ranked last in the NFL in stopping the run in 2010.

The Bills didn’t have much problem stopping it Sunday.

They didn’t have much problem with anything.

Fitzpatrick needed only five plays after McCluster’s fumble to hit Chandler from four yards out for a 7-0 lead, and Buffalo scored again late in the quarter when he hit Steve Johnson in the back of the end zone.

Even when Kansas City started to find its rhythm, things went haywire.

Cassel engineered a nice drive that looked like it would result in a touchdown pass to Pope, but the big tight end’s knee came down out of bounds while he was still juggling the ball. Then came Spencer Johnson’s sack of Cassel and Succop’s missed field goal.

Buffalo promptly went 50 yards for a field goal and a 17-0 lead, and added another field goal after Charles fumbled on the first play of the Chiefs’ ensuing possession.

The Bills scored 20 or more points four times last season; they had that many with 5:38 left in the first half Sunday.

“When things started going bad, they just went bad,” Chiefs defensive tackle Kelly Gregg said. “Landslide”

Kansas City finally mounted a scoring drive that Cassel finished off with a short touchdown pass to Charles on third down, but the Chiefs still trailed 20-7 at halftime.

“Any time you score only seven points and your opponents put up 41, you’re not having an effective day,” Cassel said. “We’ve got to get back on the drawing board.”

Chandler added his second TD grab after halftime, which came after a pair of penalties turned third-and-goal at the one foot line into third-and-goal at the 11. Fitzpatrick added his fourth touchdown toss of the game to Donald Jones later in the third quarter.

There was a somber atmosphere at Arrowhead most of the day, and not just because of the score. As one of the main venues selected by the NFL for Sept. 11 tributes, a field-sized American flag was unfurled before the game. American Idol winner David Cook sang the national anthem, and military flyovers were conducted before kickoff and again at halftime.

“I know that we weren’t ready. The Buffalo Bills were better prepared today than the Kansas City Chiefs,” Haley said. “We got to be better next week, but for today, we were not prepared. And I’m taking full responsibility for that.”

Notes: The Chiefs were 7-1 at Arrowhead last season. … Kelvin Sheppard’s recovery of McCluster’s fumble was the first by a Bills rookie in a season opener since Dan Jilek and Ken Jones each had one against Miami on Sept. 13, 1976. … Chiefs S Eric Berry left in the first quarter with a knee injury. … Bills CB Terrence McGee also left in the first quarter with a hamstring injury.