The Philadelphia Eagles are poised to do something no other No. 1 seed ever has -- begin the playoffs as an underdog.

The Atlanta Falcons opened as 2.5-point favorites over the Eagles in Saturday's divisional round game in Philadelphia.

Since 1975, when the NFL began basing home-field advantage on teams' regular-season winning percentage, no No. 1 seed has ever been an underdog in its first playoff game, according to ESPN Stats & Information. Barring dramatic line movement, the Eagles will be the first.

The Eagles lost quarterback Carson Wentz to a knee injury in early December and haven't looked the same team with backup Nick Foles under center.

Westgate Superbook oddsmaker Ed Salmons estimates the Eagles, with a healthy Wentz, could have been as much as 6.5-point favorites over the Falcons. Without him, Salmons and other Las Vegas oddsmakers say Philadelphia would be an underdog to any other team in the NFC playoffs this week.

The Falcons beat the Rams 26-13 Saturday to advance and now head to Philadelphia as the first No. 6 seed to be favored in the divisional round.

Since the NFL went to a 12-team playoff format in 1990, only four No. 1 seeds have been less than 3-point favorites in their first game. Most recently, the 2010 Falcons were only 1-point favorites over the Green Bay Packers in a divisional game. The Packers won 48-21.

Bettors were siding with the Falcons over the Eagles early. The line had already grown to Atlanta minus-3 on Sunday morning at some sportsbooks.

"The early action, it's pretty much all on Atlanta," Salmons told ESPN on Sunday.. "The public is going to bet Atlanta."

Las Vegas sportsbook operator CG Technology also reported early interest in the Falcons.

"We might not take a bet on the Eagles until it hits (Atlanta minus) 3.5," CG Technology's Jason Simbal said.