Janoris Jenkins

Giants cornerback Janoris Jenkins has shut down opposing receivers this season. (Erich Schlegel-USA TODAY Sports)

EAST RUTHERFORD -- Janoris Jenkins was largely a mystery to his teammates when he signed a five-year, $62.5 million free-agent contract with the Giants in March after four seasons with the St. Louis Rams.

Linebacker Jonathan Casillas has bounced around the NFL during his eight-year career, but he admitted that he had no idea how good Jenkins was until the cornerback took the field in practices this offseason.

"He had to be some type of player to get that type of deal," Casillas said. "But within a few months, I realized that this dude is top tier, top 2-4 in league, and he's been proving that week in and week out."

Safety Landon Collins took a more proactive approach, watching film of Jenkins after after getting word the Giants were targeting him in free agency.

"I had to get some feedback," Collins said, "because everybody was coming up to me like, 'You got Jackrabbit, he's a dog!' I was like, 'For real? Let me go see what the hype is about.' And when I went to see the hype, I was like, 'Yeah, he's the man.' "

Cornerback Coty Sensabaugh had noticed Jenkins on film in the past while scouting opposing wide receivers. But Sensabaugh didn't truly appreciate Jenkins' talent until joining the Giants in October.

"I think seeing somebody on film or TV is one thing. And then when you're actually with them every day, you truly can appreciate them," Sensabaugh said. "I think the best thing about Janoris that a lot of people don't realize is he's super smart. He's one of the smartest corners I've played with."

Defensive coordinator Steve Spagnuolo had a better idea about Jenkins' ability because cornerbacks coach Tim Walton was the Rams' defensive coordinator in 2013.

"We had a wealth of information," Spagnuolo said. "Tim was convicted about Jackrabbit and he convicted us and away we went."

Even with that first-hand knowledge, signing Jenkins to a big-money contract was a risk. Even Jenkins admitted that he lost focus and got "lazy" at times during four losing seasons with the Rams.

But Jenkins has been locked in during his first season with the Giants. He has been tasked with covering opposing No. 1 receivers all season and he has met the challenge.

Jenkins turned in his most dominant performance of the season in last Sunday's 10-7 with over the Cowboys. He shadowed Dez Bryant and held the Cowboys' most dangerous receiver to one catch for 10 yards. Jenkins forced a fumble on Bryant's one catch and also had an interception.

"He has all the great qualities a shut-down corner would need to have," rookie cornerback Eli Apple said. "He's quick, he's fast, physical, good motor."

The 5-foot-10, 198-pound Jenkins, 28, has the versatility to cover Pittsburgh's 5-foot-10, 181-pound Antonio Brown and Cincinnati's 6-foot-4, 210-pound A.J. Green.

"Him being undersized as a corner and playing bigger receivers and playing great ball against them, that's phenomenal," Collins said. "You don't see those types of guys. Those are the types of guys that usually get picked on. He just plays the game like it's him and that person and he's not allowing them to catch the ball."

In addition to his physical skills and competitive mindset, numerous teammates identified Jenkins' football IQ as his greatest asset.

"I don't want to say he knows what's coming, but his instincts -- I don't know if it comes from film study or him just knowing football," Sensabaugh said. "But that really surprised me when I got here, how smart he is."

Jenkins' ability to matchup with the opponent's top receiver has had a major impact on the rest of the defense.

"You know you have one side of the field shut down," Collins said. "You don't have to worry about it. If it's man-to-man coverage, deep balls, anything like that, it's possible it could be a turnover. It's a breath of fresh air. It's a blessing and we're all thankful for that."

There were signs that Jenkins was capable of this level of play while in St. Louis and the Giants' front office clearly recognized them. Now, the rest of the football world is catching on.

"I feel like I had been doing it in St. Louis. But St. Louis is St. Louis," Jenkins said. "I'm just glad to be here in New York where the lights shine bright and everybody gets to see you."

Dan Duggan may be reached at dduggan@njadvancemedia.com. Follow him on Twitter @DDuggan21. Find our Giants coverage on Facebook.