PHILADELPHIA — The Philadelphia Eagles turned in their worst offensive performance of the Chip Kelly era in Sunday’s 24-14 loss to the Seattle Seahawks.

They had just nine first downs and 139 net yards and converted only 2 of 11 third-down opportunities. Four of their 13 possessions were three-and-outs. Two others ended in turnovers after just one play. The Eagles ran just 45 plays and had the ball for only 18:04.

“We couldn’t get into a rhythm,” Kelly said. “First drive, three-and-out. We missed on two pass plays then came up just short on our third-down conversion.

“Our third possession, we throw a pass on first-and-10 that was incomplete, then on second-and-10, we have a six-yard loss on a run play (by Darren Sproles) because there was a miscommunication up front.

“We obviously were in too many third-and-longs all day long to put yourself in successful situations. It’s a lot easier when you’re in third-and-medium, third-and-short. Way too many third-and-longs yesterday.”

Kelly dismissed a question from a reporter wondering whether he considered playing at a slower tempo against the Seahawks and using up more clock time.

“Time of the play doesn’t matter,” he said. “Even if it takes five minutes to run three plays, if you don’t execute, you’re still going off the field. You have to execute to stay on the field.

“It’s about plays run. Time of possession, I don’t understand that concept. It’s plays run. They ran 83, we ran 43. We need to run more. And that means we need to convert on third down. And it means defensively, we also need to get them off the field on third down.”

Sunday’s game against Dallas likely will decide the NFC East. It’s also very possible that the loser, even if they win their final two games and finish 11-5, could miss the playoffs.

Asked Monday about his team’s ability to bounce back from Sunday’s tough 10-point loss to the Seahawks, Kelly said: “You’re going to have days when you’re really successful and you’re going to have days when it doesn’t work out the way you want it to work out. But are you going to pack your bags after that and take your ball and go home? I don’t think we have a group like that.

“This team has good resolve. I expect them to be flying high when they get in here tomorrow and be ready to go. There’s no better way to get their attention than playing the Dallas Cowboys at home in front of our crowd. I think they’ll be fired up for it.”

NOTES: ILB Emmanuel Acho was active Sunday after missing the Eagles’ Week 14 game against Dallas with a groin injury. But he played just two defensive snaps. Casey Matthews took all of the rest. … QB Nick Foles missed his fifth straight game with a broken collarbone. Chip Kelly said there was no update on him. He is expected to be examined again next week.

REPORT CARD VS. SEAHAWKS

PASSING OFFENSE: D-minus — Aside from his two touchdown throws to Zach Ertz and Jeremy Maclin, it wasn’t a very good day for Mark Sanchez. He completed just 10 of 20 passes for 96 yards and had a bad interception in the fourth quarter that pretty much closed the door on any Eagles victory hopes. The Legion of Boom did a good job of taking away his receivers.

RUSHING OFFENSE: D-minus — The Eagles’ ground game is the straw that stirs Chip Kelly’s offensive drink, and it just didn’t stir very well Sunday night. LeSean McCoy, who had rushed for 289 yards in the previous two games, averaged just 2.9 yards per carry and had a costly fumble at the beginning of the second half. The Eagles had just three rushing first downs.

RUN DEFENSE: B — Led by Fletcher Cox, who might have had one of his best games as an Eagle, the defense did a pretty good job of neutralizing Marshawn Lynch. He had a 21-yard run on a third-and-15 on the Seahawks’ first possession, but was held to 65 yards on his 22 other carries. Russell Wilson burned them on an early zone-read, getting Trent Cole to crash down on Lynch and then running 26 yards for Seattle’s first touchdown.

PASS DEFENSE: C-minus — For the 11th time in 13 games, the Eagles gave up multiple touchdown passes. Sacrificing sack opportunities to keep Russell Wilson in the pocket, the Eagles’ secondary often struggled to stay with their coverage. They also got caught napping on a roll-right-throw-back-left touchdown pass to Lynch in the third quarter. Bradley Fletcher also got flagged for a 44-yard pass-interference penalty that set up that touchdown.

SPECIAL TEAMS: B-plus — The Eagles’ coverage units had an outstanding game. KR Josh Huff had a 46-yard return in which he fumbled three different times and barely managed to retain possession. The Eagles nearly blocked two Jon Ryan punts. Donnie Jones had a 43.3-yard net average on eight punts.

COACHING: Grade: C — Bill Davis’ unit did a good job of neutralizing Lynch, and used a mush rush to try and keep Russell Wilson in the pocket. Kelly’s offense had its worst day in his two seasons as Eagles coach. He curiously punted on a fourth-and-11 with four minutes left and his team down by two scores.