With the country still in shock after Kansas City linebacker Jovan Belcher killed his girlfriend then committed suicide, the struggling Chiefs (2-10) kept their emotions in check to beat the Carolina Panthers (3-9) 27-21 at Arrowhead Stadium.
"We do have a lot of guys who are really hurting," the struggling team's chief executive officer Clark Hunt said.
"I told them 'There's not a lot I can say to you other than we're family and we have got to pull together right now and support each other.'"
The game added a sombre touch to one of the toughest leagues in the world. The NFL is no place for the faint-hearted and on most days, the only thing that matters is the win-loss column.
The New England Patriots, the Houston Texans and the Denver Broncos all won on Sunday to book their spots in the play-offs with four weeks to spare.
The Atlanta Falcons also advanced to the postseason, leaving eight places up for grabs, when they clinched the NFC South Division after they won on Thursday and Tampa Bay lost on Sunday.
The Baltimore Ravens (9-3) missed their first chance to qualify when they were beaten 23-20 by their AFC North division rivals the Pittsburgh Steelers (7-5).
The San Francisco 49ers and Chicago Bears both lost in overtime, defeats that could come back to hurt when seedings for the play-offs are decided, but the Green Bay Packers and Indianapolis Colts were celebrating after recording victories that left them on the verge of making the postseason.
The Patriots (9-3), last season's beaten Super Bowl finalists, clinched the AFC East division with a 23-16 win over the Miami Dolphins (5-7) in Florida.
It was the sixth win in a row for the Patriots and the ninth time in the past 10 years they have won their division.
"It's good to get another division win. We accomplished one of our goals this year, to be in the postseason," said New England head coach Bill Belichick.
"That's good, but more importantly we just gotta keep working to get better. We still got a lot of football left to play."
The Texans (11-1) also chalked up their sixth straight victory, beating the Tennessee Titans (4-8) 24-10 to secure their spot in the play-offs, although they have still not clinched the AFC South division.
The Colts (8-4) stayed in touch with an extraordinary 35-33 comeback win over the Detroit Lions (4-8).
Rookie quarterback Andrew Luck passed for 391 yards and four touchdowns, including a 14-yard touchdown pass to Donnie Avery as the game clock expired to hand the Colts the victory after the Lions led by 12 in the final quarter.
The Broncos (9-3) wrapped up the AFC West title for the second year in a row after beating the Tampa Bay Buccaneers (6-6) 31-23, with quarterback Peyton Manning throwing for 242 yards and three touchdowns.
The Packers (8-4) joined Chicago at the top of the NFC North standings with a 23-14 win over Minnesota Vikings (6-6) at Lambeau Field with Aaron Rodgers completing 27 of 35 passes.
Rookie kicker Greg Zuerlein converted a 54-yard field goal with 26 seconds left in overtime to hand the St. Louis Rams (5-6-1) a 16-13 victory over the 49ers (8-3-1), just three weeks after the two teams played out the first NFL tie in four seasons.
Rookie quarterback Russell Wilson threw a 13-yard touchdown pass to Sidney Rice to give the Seattle Seahawks (7-5) a 23-17 overtime victory over the Bears (8-4) in overtime.
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