NEW YORK — That gaudy 6-0 record the Denver Broncos held in October has faded under an avalanche of weak performances. Unless they win Sunday and get some help, the Broncos will be watching the postseason, not participating in it.

When the Giants stormed to a 5-0 mark, talk of winning a second Super Bowl in three years dominated the New York football scene. Two months later, the Giants are 8-7 and out of contention.

Never has it been more clear in the NFL that it's how you finish that matters. The Giants learned that lesson painfully and are also-rans. The Broncos could be joining them, along with the Bears (3-1 to 5-9), 49ers (3-1 to 7-8), Falcons (4-1 to 8-7), and possibly the defending champion Steelers (6-2 to 8-7) .

Baltimore and the New York Jets each began 3-0. They are 8-7, but unlike Denver and Pittsburgh, victories on Sunday against Oakland and Cincinnati, respectively, earn them wild-card spots.

"We have a great opportunity in front of us," Jets running back Thomas Jones said. "It's so funny how things can change in a week in this league."

Not so funny to the Broncos, who could become the third team since the 1970 merger to go from 6-0 to not making the playoffs, joining the 1978 Redskins and the 2003 Vikings.

"I'm frustrated because I think we've done some great things this year, but we didn't finish off well," said Broncos defensive end Elvis Dumervil, the NFL sacks leader. "To be able to win in the NFL, you have to be consistent for 60 minutes, times 17 weeks. It's like growing pains, we've just got to continue to fight through it.

"If we're more consistent, we start fast and finish strong instead of slumping again at the end like this."

Meanwhile, the fast closers are quickly becoming part of the Super Bowl conversation, from San Diego, which has won 10 in a row, to Philadelphia (six straight) to Green Bay (six of seven). Not that anyone is dismissing Indianapolis, which just took its first loss after 14 victories — and led the Jets before pulling many starters — New Orleans or Minnesota from the conversation.

But there's no denying the Chargers, Eagles and Packers are surging. The Saints, Vikings and Bengals are not.

"There's really no explanation for the way we played over the past couple of weeks," Vikings safety Madieu Williams said after his team was beaten by the Bears on Monday night. "We have to go back to the drawing board."

And conjure up something, quickly.

Like their division rivals, the Packers, have done.

Green Bay slipped to 4-4 before a mid-November victory over Dallas. In that game, the 3-4 defense the Packers switched to this season began taking hold. The offensive line was solidified when tackles Chad Clifton and Mark Tauscher got healthier.

"We had a sense of urgency and minor desperation, I think, starting with the Dallas game, and got on a roll," quarterback Aaron Rodgers said. "Defensively, those guys started believing in each other, believing even more in Dom (Capers, the coordinator) and his strategy, and we've got an MVP candidate (Charles Woodson) on defense. Charles has really taken over games at different points during this run we've been making. And offensively, I think we've figured out some things as well."

Figuring out why some teams fade and others soar heading toward the playoffs is no simple matter. Looking at this season, though, here are some critical factors in the rise of some and the fall of others.

—Health. As noted, the Packers got back two key ingredients on their offensive line. San Diego star running back LaDainian Tomlinson recovered from an ankle problem.

But the Giants lost middle linebacker Antonio Pierce, their defensive leader, and their secondary has been ravaged. Powerful running back Brandon Jacobs has been nicked up all year and never ran with typical abandon.

The Steelers' seven losses all came with wrecking ball safety Troy Polamalu either hobbled or sidelined. Atlanta couldn't survive injuries to Matt Ryan and Michael Turner, the core of the offense.Of course, some teams have prospered despite injuries, particularly Philadelphia, leading to ...

—Depth. The Eagles barely have had the services of star running back Brian Westbrook in 2009, yet rookie LeSean McCoy and versatile fullback Leonard Weaver more than filled the void. Philly is a passing team, too, and Donovan McNabb never has had such a deep group of targets.

Green Bay and San Diego also have plugged in previously unproven players such as tight end Jermichael Finley (Packers) and wide receiver Legedu Naanee (Chargers) and not missed a beat.

The Giants' defense fell apart in part because the backups showed why they are backups, becoming a liability when given extensive playing time. Same for the quick-starting Bears.

—Experience and continuity. The Chargers and Eagles have traveled this path before, as recently as last season. San Diego rallied past collapsing Denver to win the AFC West and then beat the Colts in the wild-card round. Philadelphia won four of its final five games in 2008, then came within one defensive stand of making the Super Bowl.

Both franchises have had stability in the front office and in coaching. So has Green Bay. Players who are comfortable with the system, their assignments and the coaches' methods usually prosper.

The Giants had those pluses in their favor, too, but the other factors overwhelmed them. Denver, Atlanta and San Francisco did not.

Indeed, the Broncos had the wrong kind of memories stuck in their mind.

"We have a totally different scheme, different personnel, different guys upstairs, so it's not really the same team," Dumervil said. "It's the same situation, different year."