Fletcher Cox and Mychal Kendricks first met in April 2012 during a predraft visit to Tennessee. They took a limousine together to the Nashville airport. They were not the most compatible pair of 21-year-olds to share a 20-minute ride.

Cox is from Yazoo City, Miss.; went to college at Mississippi State; and likes to spend his free time taking his ATVs "mud-riding." Those who know Cox describe him as a "big ol' country boy." Kendricks grew up in Fresno, Calif.; went to the University of California; and collects hats and shoes. He once attended a private school that specializes in fine arts.

"I noticed he wasn't from my side of the world," Kendricks said. "When I'm asking him questions because we could be on the same team . . . he's talking about mudding . . . and catching fish. All this country stuff. I just thought he was a weird dude."

Cox laughed when recounting the ride. His recollection was similar - two players from different parts of the country who knew little about each other, both riding the speculative confidence of the predraft hoopla.

"It was kind of weird at first," Cox said.

They became teammates later that month when the Eagles drafted them both as potential foundation pieces on their defense. Cox was the No. 12 overall pick. Kendricks came one round later with the No. 46 overall pick. They've been linked ever since. Together, they have endured coaching and scheme changes, the weight of expectations, and the reality of criticism.

They're still young - both are only 23 - and are in their third NFL seasons. If they thrive in Philadelphia, there could many more games like last week's win over the Jacksonville Jaguars.

Cox finished with six tackles and a fumble recovery for a touchdown, seemingly a constant presence in the Jaguars' backfield. Kendricks finished with six tackles, a sack, a quarterback hit, a tackle for a loss, and a pass deflection.

The Eagles did not make any sweeping roster changes to one of the NFL's worst defenses in 2013. They instead relied on returning players improving in their second year in defensive coordinator Bill Davis' scheme. Cox and Kendricks are looking like the foundational pieces they were expected to become.

"They are frontline players," linebacker DeMeco Ryans said. "Those two guys, back three years ago, were great pickups for us. They've shown that. They're becoming mature pros, and it's shown out on the field."

Learning the system

When Davis accepted the job before the 2013 season, his pledge was to give every player a blank slate. Cox and Kendricks represented intriguing young talent, although Davis was not involved in the organization's selecting them.

They were selected for a different scheme - with Jim Washburn as the defensive line coach and Juan Castillo as defensive coordinator - and became immediate contributors. Then they needed to transition from a wide-nine alignment that emphasized linemen going upfield and often left blockers on linebackers, to a two-gap, 3-4 alignment that required linemen to occupy blockers and freed up space for linebackers.

"It benefits me a whole lot more, but [Cox] is not getting to the quarterback as much, and he didn't understand the patience of it at first," Kendricks said. ". . . Going into that the second year to the new program, to the new scheme, it was an adjustment for all of us."

When Cox was a rookie, Washburn declared that "when God made him, he meant him to play in this system right here." A year later, the Eagles needed Cox to play a different style. He could still use the gifts that made him such an enticing prospect - at the 2012 combine, he ran a 4.79-second 40-yard dash at 6-foot-4 and 298 pounds and with 341/2-inch arms. He just needed to use them in a different way.

"I think Fletcher can play in any scheme you throw at him," Davis said. "It's not only two-gap. It's not only wide-nine. It's not only three-gap penetrating. I think he's got a very well-rounded skill set, the run game, the pass rush."

Cox has a better grasp of how to transition on a given play from defending against a run to defending a pass. Coach Chip Kelly said it's because Cox no longer worries about where he's lining up, which is a by-product of experience in the scheme.

"Last year I think I struggled a little bit, adapting to the different position and different responsibilities I had," Cox said. "But I [have] another offseason under my belt, another training camp."

Kendricks' hallmark is speed. He was the fastest linebacker in the 2012 draft. But the mind needs to slow down for the body to play fast. As his understanding of the scheme improved, Kendricks was used more as a blitzer or even as a fourth pass rusher. It's a skill he showed last week.

"He's playing faster, but he still can grasp the defense to another level," Davis said. "Mychal is a phenomenal athlete that can make a lot of plays, but [you] unleash that ability to make plays when your brain is working slower and it comes easy to you."

'Sky's the limit'

The leap that players often take from their first year to their second year was stunted for both players. Only a part of their rookie experience was applicable in their second year. Now that it's their second time around in Davis' defense, that progress is evident - especially for Cox, who had more of a dramatic change and has such tantalizing ability.

"You can look at it as our second year in the same defense," Cox said. "If we were in the same defense three years in a row, then I think the production would be" even more advanced.

Kelly does not like to talk about a player's ceiling. He used Peyton Manning as an example of how a player, no matter how good, can always improve. But Cox and Kendricks seemed to be the two defensive players last season with the greatest room to improve.

Teammates are noticing. Ryans said Cox was "dominant up front" last week, and linebacker Connor Barwin said it's the by-product of growth that started to show at the end of last season. Barwin emphasized that there should be no surprise with the way Cox played.

"I think you're going to see what Fletcher did Sunday for the rest of the year," Barwin said. "Now, he knows what to do, how to do it, and is fully confident in what he's doing. And when you play that way, you can play a lot more physical and a lot faster."

Ryans, who plays next to Kendricks, said that Kendricks is "playing at another level" because of how he understands the system. He has the ability to make plays rare for a linebacker.

One game is not enough for a coronation. But if the Eagles defense improves this year, it will be with Cox and Kendricks as the linchpins. A relationship that started with little to talk about in a limousine in Nashville has become one that could bolster the Eagles defense for years to come.

"Sky's the limit," Kendricks said. "There are only a few players who have their jerseys retired. But what's wrong with dreaming?"