Overpaid.

That was the immediate reaction around the league when the Giants signed Janoris Jenkins to a five-year, $62.5 million contract. Jenkins was considered a skilled cornerback, not elite, prone to big plays in his four years with the Rams but too much of a gambler, a risk-taker who gave up too much too often to the opponent.

For one game, his first with the Giants, Jenkins was worth every cent.

Jackrabbit, as he prefers to be called, put in a full day’s work in the Giants’ 20-19 season-opening victory over the Cowboys. He was the only defensive player to stay on the field for all 78 snaps — quite the workload, considering the Cowboys had the ball for nearly 37 minutes and put together drives of 15, 15 and 11 plays on their first three possessions, all resulting in field goals despite twice driving inside the Giants’ 10-yard line.

There was no easing in for Jenkins in his first game with his new team. He was entrusted to cover Dez Bryant almost all game, and Bryant was no factor, with one catch for 8 yards. Dak Prescott, the rookie quarterback, threw at Bryant only five times. He went deep when safety Landon Collins was lined up against Bryant — not a good matchup for the Giants — and might have had a 24-yard touchdown if Bryant were able to maintain possession as he hit the turf in the end zone.

Dominique Rodgers-Cromartie, mostly lined up in the slot, matched up a few times with Bryant as well. This was a Jenkins-Bryant duel, though.

Ben McAdoo in the early stages of his head-coaching tenure has not exactly gushed about anyone or anything too often, but he was quick to single out Jenkins after seeing him in play for the Giants for the first time in the regular season.

“Janoris had a heck of a day,” McAdoo said Monday. “He’s not the only one that was matched up against Dez. DRC made a couple of nice plays there, too. But Jackrabbit really shadowed him for most of the day and competed his tail off. It was a big, huge effort for us.”

These sorts of defensive exploits were few and far between for the Giants in 2015 and the major reason they invested nearly $200 million to sign Jenkins and linemen Olivier Vernon and Damon “Snacks’’ Harrison. All three came up big in their Giants debuts. None came up bigger than Jenkins.

“I think we did OK,” Jenkins said after the game. “There is always room for improvement as far as stopping the run, getting off the field on third down.”

Jenkins, 27, is not one of those flashy cornerbacks who takes as much delight talking about the plays he makes as he does making them. He was a quiet addition in the spring, summer and throughout training camp, getting his work in without any fanfare. He aced his first test, keeping Bryant from getting any traction, although there is no doubt Prescott in his first NFL game was operating on training wheels, looking to dump the ball down to tight end Jason Witten and Cole Beasley on inside slants rather than test the Giants deep.

Rodgers-Cromartie was a bust when forced to play the slot with the Eagles, but he’s accepted that role with the addition of Jenkins and the selection of Eli Apple in the first round of the NFL draft.

“We like him there,” McAdoo said of DRC in the slot.

As for Apple, his NFL debut went as so many of them do with rookies — unevenly.

“He was feeling his way early and got his feet underneath him and really competed at a higher level as the game wore on,” McAdoo said. “Just like a lot of young players, they have to be able to feel their way a little bit at times and play through it.”

There will be stiffer tests in terms of passing attacks, starting with Sunday’s home opener against Drew Brees and the Saints. These teams tangled last season in New Orleans, and the result was a defenseless 52-49 Saints victory in a wild shootout. It was no shock the Saints opened this season with a wild 35-34 loss to the Raiders, coming up short despite four touchdown passes and 423 passing yards by Brees, throwing primarily to Willie Snead and Brandin Cooks.

So the solid showing in Game 1 will give way to an entirely different challenge for the Giants secondary in Game 2.