Redskins receiver Josh Doctson drops a fourth-quarter touchdown that would have given Washington a seven-point lead. (John McDonnell/The Wahington Post)

Like an adolescent grappling with growing pains, the Washington Redskins have flashed multiple personalities through the early stages of the NFL season.

Monday night’s meeting with the Kansas City Chiefs, the NFL’s only remaining unbeaten team, represented an athletic truth serum of sorts — a game that would reveal whether Coach Jay Gruden’s squad was the ill-prepared bunch that couldn’t tackle or run the ball in their Week 1 loss or the splashy defenders and precision offense that throttled Oakland in Week 3.

The Redskins were all of the above in spots — but ultimately not good enough — in a thriller that wasn’t decided until the final four seconds, in which the Chiefs hit a game-winning 43-yard field goal, then tacked on a touchdown following a fumbled lateral sequence for a 29-20 victory.

The contest was closer than the score indicated, with the Redskins bolting to a 10-point lead on the strength of hard-hitting defense and an offense that’s still coming into form. But as their injuries mounted and sloppy penalties piled up, the Chiefs seized control in the second half, playing a game of keep-away as they chipped at the Redskins’ lead one field goal at a time.

Quarterback Kirk Cousins, who was 14 of 24 for 220 yards and two touchdowns, nearly connected with Josh Doctson for a game-winner with 57 seconds remaining, but the rangy second-year receiver couldn’t do enough to pull down a well-defended end-zone throw.

The Redskins then settled for a game-tying field goal, only to allow the Chiefs to avert overtime with a nine-point explosion over the final 47 seconds.

“This is the NFL’s best team, supposedly, at 4-0, [and] we gave them all they could handle,” Gruden said afterward, praising Cousins for making drive-saving plays with his legs down the stretch and crediting Josh Doctson with a terrific effect in the game-winner that wasn’t. But Gruden was clearly exasperated by the defensive penalties that gave the Chiefs new life and equally frustrated that his offense couldn’t get on the field once Kansas City’s run game got rolling.

The defeat sent the Redskins into their bye week with a 2-2 record, while the Chiefs, who out-gained the Redskins 439 yards to 331, improved to 4-0.

It was a costly loss.

Redskins cornerback Josh Norman suffered fractured ribs, Gruden confirmed after the game, and could miss several weeks. Norman had made a pulverizing hit on tight end Travis Kelce early in the game, with no apparent ill effects, setting a ferocious tone for the secondary in the process.

The collision that sent him to the locker room came on Kansas City’s first touchdown drive, when he and linebacker Zach Brown tried breaking up a 21-yard completion by Chiefs quarterback Alex Smith (27 of 37 for 293 yards, one touchdown). Norman headed to the sideline, and Smith followed with a 17-yard touchdown pass to Kelce.

It was the most consequential in a series of events that shifted the momentum in the home team’s favor during the final five minutes of the first half.

Arrowhead Stadium is among the more deafening venues in the NFL, so it was important the Redskins start fast to keep the crowd noise at bay. They couldn’t have gotten off to a better start.

Washington scored on its opening possession, leaning on a heavy diet of running back Rob Kelley until Cousins threw a change-up in the form of a deep shot in the end zone to wide receiver Terrelle Pryor. The 6-foot-4 Pryor outdueled cornerback Marcus Peters for the 44-yard reception — his first touchdown with the Redskins — and staked the visitors to a 7-0 lead.

Washington’s defense then took the field and sacked Smith, who was operating behind a patchwork offensive line, on the opening play.

The Chiefs, who boasted the NFL’s top-ranked rushing attack (162 yards per game and third-most prolific offense overall (397 yards per game), could barely get out of idle, forced to punt on their first two drives.

Cousins was efficient in getting the Redskins into the red zone on their second series, but three attempts to run the ball in for the score failed. Kicker Dustin Hopkins salvaged the drive with a 19-yard field goal that made it 10-0.

A smattering of Chiefs fans booed their own as Smith and the NFL’s leading rusher, Kareem Hunt, struggled to make headway against the hard-tackling Redskins.

As the first-half clock ticked down, it seemed the Redskins would head into the break with a shutout.

But their fortunes shifted on one drive. Kelley hobbled off the field with an ankle injury and didn’t return. A chance to extend their lead fizzled when Pryor couldn’t reel in a tough but catchable ball on third down.

The Chiefs took over with 5:01 remaining in the period, having amassed just 72 total yards to that point.

The Redskins lost Norman on the Chiefs’ touchdown drive that followed.

With 1:54 remaining, Gruden called three pass plays in a row and punted, giving the Chiefs another shot at scoring.

A gaffe on defense enabled Smith to scramble for a 32-yard gain before D.J. Swearinger stopped him like a jersey wall. It went a long way toward putting the Chiefs in field-goal range, but Harrison Butker, the Chiefs’ new kicker, missed the 46-yard attempt, preserving the Redskins’ 10-7 lead at the break.

It was a battered Redskins squad that returned to the field for the third quarter, missing both Norman and Kelley. In short order, linebacker Martrell Spaight (ribs) and safety Deshazor Everett (hamstring) joined the ailing.

The Chiefs, meantime, only got stronger, with Smith providing the 1-yard touchdown run that capped Kansas City’s opening drive of the second half.

Cousins immediately countered, putting the Redskins back on top, 17-14, with a 3-yard strike to Ryan Grant.

From there, Chiefs Coach Andy Reid turned it into a ball-control contest. Hunt carried often and effectively, gobbling up the clock on successive drives that topped the seven- and eight-minute marks and produced a tying field goal and a go-ahead field goal with 4:51 remaining.

Less than a minute remained when Cousins, on a third-and-2, heaved the end zone throw to Doctson and watched it roll away from his grasp.

Hopkins tied it at 20 apiece, leaving the Chiefs 47 seconds. It was enough.