The Super Bowl 50 champions began this season 4-0, and then it all fell apart.

The Broncos’ attempt to defend their Super Bowl championship came to an end Sunday night at Kansas City’s Arrowhead Stadium. But their season fell apart in pieces after a 4-0 start. A look at some of the key moments:

SEPT. 8 Win vs. Carolina, 21-20

Takeaway: The Broncos were underdogs at home to open the season, but beat the Panthers for the second time in nine months. C.J. Anderson rushed for 92 yards and a score. Rookie fullback Andy Janovich scored on the first carry of his NFL career.

Key number: 83. Denver’s No-Fly Zone defense held Carolina quarterback Cam Newton to 83 aerial yards in the second half, on 7-of-16 passing.

OCT. 9 Loss vs. Atlanta, 23-16

Takeaway: After starting 4-0, the Broncos’ first loss exposed some significant cracks in their armor. The Falcons won on the road by targeting the middle of Denver’s defense, using running backs and tight ends on short passes over the middle to gain huge chunks of yardage. Broncos rookie quarterback Paxton Lynch, starting in place of the injured Trevor Siemian, struggled.

Key number: 132. The Falcons’ leading receiver was running back Tevin Coleman, who caught four passes for 132 yards. Denver’s defense had trouble adjusting.

NOV. 6 Loss at Oakland, 30-20

Takeaway: The balance of power in the AFC West took a seismic shift as the Raiders beat up Denver, exposing more weaknesses. Oakland’s offensive line steamrolled the Broncos to the tune of 218 yards rushing.

Key number: 33. While Oakland ran wild, the Broncos’ ground game fizzled. They finished with only 33 yards rushing, led by Devontae Booker’s 22.

NOV. 13 Win at New Orleans, 25-23

Takeaway: The Broncos rebounded from the loss to Oakland with a near-miracle finish. The Saints were kicking the goahead extra point late in the game when Justin Simmons leaped over the line to block the kick. Fellow rookie Will Parks caught the deflection and returned it for Denver’s winning two points.

Key number: 8. Siemian connected with eight receivers while throwing for 258 yards, led by Demaryius Thomas’ eight receptions for 87 yards.

NOV. 27 Loss vs. Kansas City, 30-27, OT

Takeaway: The Broncos’ last legitimate chance to stay alive in the race for the AFC West title slipped away when Brandon McManus missed a 62-yard field goal in overtime and the Chiefs soon after kicked the winning field goal. The Broncos blew numerous chances to put the game away; Kansas City scored eight points in the final seconds of regulation to send the game into overtime.

Key number: 5. The Broncos went 26-9 in the AFC West while winning five consecutive division titles through last season. But after the loss to the Chiefs, they were 1-3 in the AFC West this year.

DEC. 18 Loss vs. Patriots, 16-3

Takeaway: A loss in the previous week to the Titans at Tennessee put the Broncos’ playoff chances on life support, but a loss at home to New England removed all control from the Broncos. They needed to win out and get help. Denver’s offense moved the ball well early, but Siemian threw an interception that turned the tide early in the second quarter.

Key number: 13. The Broncos’ offense disappeared in back-to-back losses, rushing for just 18 yards against the Titans and scoring just 13 points in two games.