FOXBORO — As unfamiliar as the Eagles seem, the Patriots have seen them before. They just happened to be dressed as Chiefs.

Eagles coach Doug Pederson, who was Andy Reid’s offensive lieutenant in various capacities from 2009-15, runs a scheme that troubled the Patriots once already this season when they lost their home opener to the Chiefs. Principally, through a variety of looks, their entire goal is to keep the defense off-balance, and that’ll be the Patriots’ greatest challenge in Super Bowl LII.

“We’ve got to trust that the guy next to us is doing his job because you can’t do two things at once against this offense,” safety Devin McCourty said. “If they run outside, they have a play that balances it up and looks the same, and they’ll run it inside. If they usually throw the ball on a slant route on this look, they’ll have a play where the slant is there but they’ll also have a wheel route to the outside.

“They have so much balance in the run and passing game.”

Backup quarterback Nick Foles has been successful in the quirky system, much like Alex Smith with the Chiefs. The key for the Patriots will be to bottle up his first read and force him to plod his way through the rest of his progressions. That’s when Foles has gotten into trouble because he doesn’t anticipate as well, which is why he has been a backup at every stop of his career.

Thing is, the Eagles are aware of that, and they’ll present a host of different looks with the attempt to keep the Patriots on their heels, whether they use wide receiver Nelson Agholor in motion in the backfield, start tight end Zach Ertz next to Foles in the shotgun or deploy an array of stacked and bunch formations to test the defensive communication.

“Everyone has to do a job for the defense because that’s how the defense is good,” McCourty said. “If you don’t do it or you leave a gap uncovered, they have too many talented players that you can’t just say, ‘Let’s stop (Alshon) Jeffery and not worry about Nelson Agholor and Torrey Smith.’ They’ll kill you, too.

“You can’t stop just Ertz because he’s a receiving tight end and think (Trey) Burton won’t get vertical on you and hurt you the same way. We have to play balanced on defense.”

It’s important to put Foles’ resume in context. Aside from the Eagles’ meaningless regular-season finale against the Cowboys, the worst of his five starts occurred on national television against the Raiders on Christmas, which directed the doom-and-gloom narrative of the Eagles’ impending demise, which obviously never came.

He then completed 23-of-30 passes for 246 yards and a 100.1 passer rating in the playoff opener against the Falcons, though some wayward throws led to early struggles for the offense. That’s when running back Jay Ajayi picked up the slack, so the Patriots’ run defense has to be on point, both with the downhill calls and the options.

“I think it comes down to playing football at the end of the day,” linebacker Kyle Van Noy said. “Everyone does a bunch of different things. You need to be able to do the little things well. That’s what this game is going to be about.”

On Sunday, Foles lit up the Vikings by completing 26-of-33 passes for 352 yards, three touchdowns and a 141.4 rating, which was the second highest ever for a starting quarterback against coach Mike Zimmer’s Vikings, who ranked first in points and yards allowed in the regular season. However impressive, the Vikings were overrun by sloppiness, particularly with missed tackles. Backup cornerback Terence Newman, who temporarily replaced an injured Xavier Rhodes, blew a coverage on Jeffery’s 53-yard touchdown reception, and corner Trae Waynes fell asleep on Torrey Smith’s 41-yard scoring catch.

So naturally, the Patriots can’t repeat some of the same mistakes that crushed them in the opener against the Chiefs, because they’ll look like the Vikings if they do. But a game from five months ago that was rife with miscommunication, poor effort in the fourth quarter and failed execution shouldn’t yield nightmarish foreshadowing. They’ve cleaned up most of the communication woes, though there were a few ugly breakdowns in zone coverage against the Jaguars.

To key on some matchups, safety Patrick Chung will take Ertz, who is the Eagles’ leading receiver, in the best one-on-one showdown of the game. Against tight ends this season, Chung has allowed an average of 1.3 receptions, 13.1 yards and a 54.8 completion percentage.

Agholor, who is used similarly to Chiefs wideout Tyreek Hill, might draw cornerback Malcolm Butler. Foles has completed 20 passes for 188 yards and a touchdown to Agholor in the last five games, so that’s also an important showdown. And that would leave a battle between former South Carolina teammates Stephon Gilmore and Jeffery, who has averaged a team-best 14.5 yards per catch with Foles.

The Patriots’ success needs to start on the edges because of that run-pass option offense, so this will measure linebacker James Harrison’s true effectiveness. He’ll likely see a lot of Lane Johnson, who is the best right tackle in the NFL but has gotten beat a couple times in the playoffs, including a sack against the Vikings.

Expect the Eagles to attack edge linebacker Eric Lee, who lost containment and surrendered a touchdown to Jaguars tight end Marcedes Lewis, and inside linebackers Elandon Roberts and Marquis Flowers. Again, these will come off the option reads while trying to force the linebackers to overcommit before isolating them with a running back, backup tight end Burton or Agholor if the Pats are in a zone.

That’s where the Patriots have to remain disciplined with their keys, and if they get stuck in a bad matchup due to an unavoidable, ill-timed play call, they’ve simply got to make the tackle to limit the damage. Ask the Vikings what happens to teams that don’t tackle well against the Eagles.

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