The free safety spent his first eight NFL seasons in Philadelphia, and led the team in tackles last year. The Eagles didn't attempt to sign him before a free agency spending spree designed to fuel a Super Bowl run.
In Week 1, they'll have to get past the player they cut loose, and the on-the-rise new team that dangled a four-year deal. "I was like, 'OK, here we go!"' Mikell recalled.
Here we go, indeed.
The Rams made a six-victory jump last year, leaving their doormat days behind. In Year 2 under coach Steve Spagnuolo, they were in contention in the weak NFC West until the final week and finished 7-9.
For Mikell's personal grudge match, they'll be the feisty underdogs at home against a perennial contender that arguably did the most to hit the ground running after the lockout.
"They're getting all the hype right now," cornerback Ron Bartell. "But no trophies are given away in September."
The Rams' free agent class can't match the Eagles' haul, but they upgraded on offense with guard Harvey Dahl and wide receiver Mike Sims-Walker, and Mikell is among four new starters on defense. "I'm one of his biggest fans," Eagles coach Andy Reid said.
"I won't be one of his biggest fans on Sunday because we're playing him, but I'm always pulling for Quintin."
The pass rush could challenge the Eagles' young offensive line with first-rounder Robert Quinn joining ends James Hall and Chris Long.
One of the newcomers, outside linebacker Brady Poppinga, brings playoff experience from Green Bay.
"I think sometimes people almost cut themselves short, afraid to be great, afraid to be successful," Poppinga said. "I think it's a matter of recognizing that the potential is there and going with it, running for it, going after it."
Quarterback Sam Bradford's rookie year was one of the best in NFL history, although running back Steven Jackson was the key to the offense with a franchise-best sixth consecutive 1,000-yard season. Bradford enters his second season with an improved set of pass catchers and expanded playbook under new offensive coordinator Josh McDaniels.
Even before their free agent splurge, the Eagles were a franchise the Rams wanted to become. In a dozen years under Reid, the Eagles have made nine playoff appearances, won six division titles and played in five NFC championship games and one Super Bowl.
Reid gave Spagnuolo his big break, hiring him as a defensive assistant in 1999. That job eventually led to a star turn as the Giants' defensive coordinator in 2007-08 and then to the Rams' rebuilding job.
"It'll be good to see him before the game and good to see him after. In between, he'll be trying to get after us, we'll be trying to get after them, so that's how it works," Spagnuolo said. "I am very grateful to Andy for giving me a start.
"There are a lot of good coaches out there that haven't coached in the NFL."
The Eagles have stockpiled talent in a quest to end the franchise's 51-year championship drought, adding cornerbacks Nnamdi Asomugha and Dominique Rodgers-Cromartie, end Jason Babin and tackle Cullen Jenkins on defense. Wide receiver Steve Smith has taken reps with the first string, and running back Ronnie Brown and backup quarterback Vince Young add more depth on offense. All of this, and Michael Vick, too.
"Just a human videogame," middle linebacker James Laurinaitis said. "He has like seven pair of eyes."
Vick started at quarterback in the Pro Bowl and was the AP's Comeback Player of the Year, distancing himself from the jail time served from a dogfighting scandal. He developed all-around skills to go with those legs, and took advantage of top-shelf skill players DeSean Jackson, Jeremy Maclin and LeSean McCoy.
Maclin will make his NFL debut in his hometown after overcoming illness this summer.
"It means a lot," Maclin said. "Going back to when I got the news all the way to where I am now, it means a lot."
Just getting to the Super Bowl won't be enough for Vick, set to make his first opening day start since 2006.
"My expectation is to win it all, as everybody's expectations should be," Vick said. "If you don't say that, then you're saying the wrong things. We expect to win it all here and that's what we are shooting for."
Mikell said Vick's emergence is one part scheme, one part supporting cast. No disagreement from Vick.
"When you have guys around you who make you better as a player, then I think your skills and your talent will show," Vick said. "I felt like I was with a good group in Atlanta but this group that I'm with now, they do things a bit differently and we're very diverse."
Vick's legs make the defensive game plan unique for St. Louis.
"People have been trying to scheme Mike Vick since I was in high school," Long said. "There have been 50-plus coordinators try to scheme Mike Vick.
"I think our job is to be aware of the fact he's going to make some plays and just rally and try to minimize the damage. We're not going shut Mike Vick down."