KANSAS CITY, MO. — The Chiefs were without their best pass rusher, their top coverage cornerback, a stalwart on the defensive line and a reliable safety who hardly ever misses a game.

Tough way to face the potent Atlanta Falcons in the season opener.

The rag-tag Kansas City defense couldn’t slow down Matt Ryan and Co. on Sunday, and the Chiefs offense couldn’t keep up. The result was a 40-24 defeat that was only close for a half.

“It’s only one game in a long season,” said Chiefs quarterback Matt Cassel, who threw for 258 yards and contributed two touchdowns, but also committed three turnovers that led to points.

“We obviously have to make a lot of corrections and get better as a football team. We’ve got to play collectively,” Cassel said. “We’ve got a lot of resilient guys in there. We’re going to get back to work and get this thing fixed.”

The team doctors may be more valuable than the coaching staff in that respect.

Starting safety Kendrick Lewis (right shoulder), cornerback Brandon Flowers (right heel) and defensive tackle Anthony Toribio (right ankle) were inactive due to injuries, while Pro Bowl pass rusher Tamba Hali was suspended for violating the league’s substance-abuse policy.

Little wonder Ryan threw for 299 yards and accounted for four touchdowns, or that Julio Jones caught six passes for 108 yards and two scores. Tony Gonzalez even added a TD catch in his return to Kansas City, just to rub a little dirt in the Chiefs’ wounds.

“Simple and plain: They made plays, and we didn’t,” Chiefs cornerback Stanford Routt said.

Jamaal Charles had 87 yards rushing, and Tony Moeaki had three catches for 37 yards, both providing a bright spot for Kansas City. The pair of them, along with safety Eric Berry, played their first regular-season games since tearing their left ACLs last season.

They were a big reason why the Chiefs matched Atlanta most of the first half, trailing just 20-17 at the break. But a missed field goal by Ryan Succop early in the third quarter proved to be the turning point, and Atlanta scored 20 unanswered points to put the game away.

“We came out very quickly and strongly on offense,” Falcons coach Mike Smith said. “I think it took us awhile to get going on defense, but we made some good adjustments on the defensive side of the ball at halftime.”

There was no controversy surrounding the replacement officials. Both times that referee Mike Shepherd went under the hood for a video review, the original call stood.

Ryan set the tone with the Falcons’ opening series, marching 80 yards behind pinpoint passing before an 8-yard pass to Jones made it 7-0 midway through the first quarter.

The teams swapped field goals before the Chiefs answered with their own TD drive.

Cassel was 4 for 4 on the series, including a 21-yard pass to Dwayne Bowe and a 22-yard TD toss to tight end Kevin Boss, who was signed in the offseason to make precisely the kind of finger-tip grabs down the seam that got him into the end zone Sunday.

The teams kept trading haymakers the rest of the half.

Ryan connected with Roddy White three times on the Falcons’ ensuing drive, and a dump-off pass that Jones turned into a 14-yard score gave them the lead. But the Chiefs had another answer when Cassel weaved his way into the end-zone from 5-yards out late in the     second quarter.

Matt Bryant added his second field goal just before half time, but Succop banged his own 40-yard try off the upright early in the second half, shifting the momentum for good.

The Falcons’ potent passing offense marched down field, Ryan capping the drive with a 5-yard scramble for a touchdown. Three plays later, Cassel was blindsided by John Abraham and the ball squirted loose, and Stephen Nicholas pounced on it to give Atlanta the ball at the 7.

Ryan hit Gonzalez in the back of the end zone on the very next play for a 34-17 lead.

It was the first TD scored by Gonzalez in Arrowhead Stadium since he was traded to the Falcons following a 12-year run in Kansas City. And as he’d done so many times, the former college hoops player dunked the ball over the goalpost, drawing mostly boos from a crowd that once cheered him.

“It’s been like a homecoming for me,” Gonzalez said afterward. “I just want all the fans to know, ‘I love you very much and thank you for letting this day be special.”’

The Falcons didn’t give them much choice in the matter.

NOTES: Atlanta CB Brent Grimes left in the fourth quarter with a calf injury. ... Rookie DT Dontari Poe started in place of Toribio for Kansas City. ... Nicholas had a game-high 12 tackles, recovered a fumble, picked off a pass and had two pass deflections for Atlanta. ... Bryant finished 4 for 4 on FGs for Atlanta.