PHILADELPHIA (973espn.com) — The unlikely emergence of veteran cornerback E.J. Biggers has made Bill Davis' sub-packages some of the most diverse in football.

Davis played the role of whipping boy in Chip Kelly's first two NFL seasons, relying heavily on a tired, single-high safety look despite having corners like Cary Williams and Bradley Fletcher, who couldn't hold up consistently in man-to-man coverage.

Now, Davis is the toast of the town as the Eagles have morphed from an up-tempo, offensive juggernaut into a team that has won with defense, an identity far-better suited for a city that prides itself on being blue collar.

As great as Andy Reid's run was in this town, he'll never be as loved as Buddy Ryan or Jim Johnson, who both cobbled together defenses that loved to punch opponents in the mouth.

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The current Eagles aren't there yet but with Fletcher Cox making the jump from Pro Bowl-level to All-Pro up front, and a embarrassment of riches at inside linebacker if everyone ever gets healthy, Davis in inching closer to putting together that kind of unit.

As impressive as the front seven is, however, it's been the rebuilt secondary that has been the most surprising part of Philadelphia's defensive turnaround.

Walter Thurmond has taken the move from cornerback to safety like a duck to water and he and the one holdover from '14, Malcolm Jenkins, have proven to be the NFL's best back-end tandem through six games.

An offseason rife with conditioning has elevated Nolan Carroll into the starting lineup and the ex-Dolphin has proven to be the Eagles' best pure cover corner, ahead of the one disappointment among the group, $63 million free agent Byron Maxwell.

A natural zone corner, Maxwell was struggling with Davis' core philosophy early in the season but he's started to come along nicely now that the defensive coordinator feels comfortable with throwing a host of different looks at opposing offenses.

And that shift from heavy, single-high looks to a multiple coverage schemes can be directly tied to the football IQs of backup defensive backs Chris Margaos and E.J. Biggers.

"I think they're growing as a group," Eagles coach Chip Kelly said on Tuesday, a day after the 27-7 drubbing over the New York Giants. "I think early, when you get a group together, they're just worried about their job. Now it's kind of looking at the overall picture and where do they fit into the overall picture and where do they fit into the overall concept of what's going on back there.

"We've got two really intelligent safeties that get everybody lined up in Malcolm and Walter, and that really helps. And then a guy I don't think gets enough credit, E.J. Biggers, has done a really nice job for us. He's a real, real smart football player. It allows Billy to do some different things call-wise because E.J. can handle it call-wise."

The multiple looks paid dividends against the Giants when a rare cover-2 sighting in Philadelphia caught Eli Manning by surprise, resulting in a Carroll pick-six.

"We actually sat in the two-deep zone," Davis explained Wednesday. "We hadn't run it all year, and we knew, because of their quick game, that we wanted to throw some cover-2 in there, a hard, zone cove-2 two.

"And Eli is right, he saw mostly two man from us the whole time. And right about that time in the game we put the hard two in, and the guys had been working hard at it all week. And (defensive backs coach) Cory (Undlin) and the guys did a great job of ruling out all the quick game, and he threw it right into where we were hoping he would. So we stole one there, and it was fun to have the plan work that way."

It's even more fun seeing the different coverages now that Davis has become comfortable enough with his options in the sub-packages.

And it's fair to wonder if Brandon Boykin wasn't traded and rookie JaCorey Shepherd wasn't injured, would we even be seeing the more exotic looks because it's Biggers' smarts that have made Davis comfortable enough to get away from his comfort zone and start taking chances.

"What E.J. brings is a great quickness and speed, and then his intelligence." Davis said. "Again, we're doing a great job of bringing guys with high football IQs into the building, and what he allows is he can play corner, nickel or dime for us at any given snap.

"So in every game plan, we can go into it with him and Malcolm both being able to switch. Malcolm can play anything, but E.J. has got the corner, nickel and dime spots down, which is a little bit different for an offense in their identification and their protection, so that screws with them a little bit. And then the fact that he can go in and out of that helps us schematically in who we want to take away, who we give help to. So E.J. has been a real big addition."

-John McMullen covers the Eagles and the NFL for 973ESPN.com. You can reach him at jmcmullen44@gmail.com or on Twitter @JFMcMullen