EARTH CITY, Mo. -- For as long as he can remember, football came easy to St. Louis Rams cornerback Lamarcus Joyner. Until last season.

The 2014 season just so happened to be not only Joyner's toughest year in football but also his rookie season in the NFL. That the two are one in the same is no coincidence.

"It definitely was," Joyner said. "For a guy like myself who you are talking about little league, high school, college had success then had to come to the league and you see that everybody is just as good as you. It's not just 'I'm gonna go tie up my shoes on Sunday and compete.' You have to really prepare and [make] each day count. I didn't understand that coming into this game. It's a continuation of what I have to do to learn in this game."

Little more than halfway through this preseason, Joyner must now hurry that process along. After losing cornerback E.J. Gaines for the season because of a foot injury, Joyner is no longer competing for the team's nickel corner job. It's his.

"He's going to be our inside guy," coach Jeff Fisher said. "He's improving every day. He's light years ahead of where he was last year. It was all happening really fast and it's starting to slow down for him. When he knows exactly what to do, he does it very well. We're counting on him to be effective in the slot, which means as a third corner, you're probably going to play 50-60 percent of our snaps."

That Joyner is stepping into that role is really no surprise considering the Rams traded up in the second round in the 2014 draft to select him. In an ideal world, he would have embraced the role last season but a combination of mental miscues and injury issues kept him from solidifying that spot.

As a rookie, Joyner played 10 games and 263 snaps, finishing with 37 tackles, one sack, a pair of pass breakups and six penalties for 41 yards. He was the team's primary slot corner for eight of the first nine games before a groin injury kept him out a few weeks. By the time he returned, Gaines had taken over in the slot with Trumaine Johnson handling outside corner duties when the Rams used their nickel package.

When Joyner went back to watch the film in the offseason, he couldn't believe what he saw.

"It was a disgrace, personally for me," Joyner said. "If I don't owe anyone, I owe myself better than what I was putting on tape out there so I didn't want to look like that guy anymore. So I went and got my mental aspect of the game better."

Joyner's brutal honesty with himself let him know that it wasn't about being faster, stronger or more athletic than everyone else. His film study led him to the conclusion everyone in the NFL is a good athlete with those physical skills. What separates the productive players from the perennial bench warmers is the game's mental parts.

"It's the NFL," Joyner said. "It's not about talent anymore. You have to tie in talent with the mental aspect of the game. Everyone is just as good as you, if not better. So I have to do things that will keep me competitive in this game against the great receivers you have to go against every Sunday. I studied the playbook and studied my assignment all offseason and that kind of helped me out a lot."

To be sure, Joyner still has plenty of proving to do entering his second season. Listed at 5-foot-8, 184 pounds, Joyner will regularly find himself overmatched from a size perspective. That makes being sharp mentally even more important.

So far in this preseason, it's been a mixed bag for Joyner. He gave up an easy touchdown pass in the opener against the Oakland Raiders but rebounded well with five tackles and a pass breakup against Tennessee.

"I think it's definitely in all honesty, 90 percent mental and 10 percent physical," Joyner said. "I didn't understand that coming in. I thought I could just come out here, lace my shoestrings up on Sunday and compete. Whereas that's clearly not the case. I got embarrassed as a rookie out there on the field last year. I just tightened up on my mental I.Q. and I've been doing pretty well so far."