Once the second half rolled around, the Chiefs fell flat and may have flat-lined their playoff hopes in the process.
Kansas City had two key turnovers and struggled to move the ball against Arizona's defense in the second half, leading to a 17-14 loss to the Cardinals on Sunday that puts a big dent in the Chiefs' playoff chances.
"We obviously need to do a better job, take care of our business," Chiefs coach Andy Reid said. "We had every opportunity to do that today and we didn't get it accomplished."
Both teams came into the game in desperate need of a win.
Once the dominant team in the NFC, Arizona (10-3) had gone into a tailspin, seemingly clinging to playoff hopes through a rash of injuries. On the ropes, the Cardinals came through like they always seem to at home, rallying from a sluggish first half with a dominant defensive second 30 minutes to keep their place atop the NFC West.
Kerwynn Williams ran for 100 yards after being elevated from the practice squad on Thursday and Drew Stanton threw a touchdown pass for Arizona, which has won its most games since an 11-victory season in 1925.
"I ain't going to deny that we needed one big," said Cardinals coach Bruce Arians, whose team is 7-0 at home, said of the victory.
The Chiefs (7-6) may have needed it more.
They were one of the NFL's hottest teams just a few weeks ago on the heels of a five-game winning streak. A tough-to-take loss to winless Oakland set Kansas City back and last week's loss to Denver knocked the Chiefs out of the AFC West race, clinging to wild-card hopes.
The Chiefs got off to a good start against Arizona behind Charles, who was questionable after banging his knee against Denver.
He showed no ill effects against the Cardinals, racing for a 63-yard touchdown on Kansas City's third play from scrimmage. He went to the locker room after turning his ankle in the second quarter, but returned quickly to turn a short catch into an 18-yard touchdown that put the Chiefs up 14-6 at halftime.
Kansas City's defense held its ground against Arizona in the first half, holding Arizona to a pair of field goals by Chandler Catanzaro, who also sent a 36-yarder off the upright to close out the first half.
After struggling early, Stanton started to find a rhythm late in the third quarter.
Worse for the Chiefs on the Brown touchdown was what came right before. Tight end Anthony Fasano hauled in what appeared to be a 19-yard touchdown, but was called for offensive pass interference.
"Quite a swing on two plays," said Smith, who threw for 293 yards and a touchdown on 26-of-39 passing.
Kansas City crossed midfield late in the fourth quarter, only to turn it over again, this time on a disputed play.
Chiefs tight end Travis Kelce was originally credited with a 19-yard catch, but the officials ruled after review that he fumbled after being stripped by Deone Bucannon and Arizona's Justin Bethel recovered.
"Shocked. Either way it is a huge play in the game," Kelce said. "It is my job to not even give doubt or put my team in that position."
Catanzaro missed a 39-yard field goal on the ensuing drive to give the Chiefs a final chance, but they turned it over on downs to put the playoffs that much further away.
NOTES: Chiefs WR Dwayne Bowe had a highlight-reel play in the second quarter, when he caught a pass and hurdled a pair of Cardinals defenders to gain a few extra yards. ... Cardinals WR Larry Fitzgerald had four catches for 34 yards after missing two games with a sprained left knee. ... Arizona starting right CB Antonio Cromartie had to be helped off the field early in the fourth quarter after suffering a left Achilles tendon injury and did not return.