There were times when Dak Prescott must have scanned the field and seen 15 players wearing blue on defense. The Giants sacked him three times in Sunday night’s 10-7 victory over the Cowboys and hit him eight more times.

What took place up front, in and around Prescott, was impressive, but it was more the work of those inhabiting the back end that led to the demise of the rookie. Prescott witnessed, for the second time this season, what an increasing number of quarterbacks are sensing as they take aim at the Giants: Where the heck are the openings?

If this keeps up, quarterbacks in the playoffs will be wondering the same thing. If you cannot stop the pass, you do not get into the postseason and certainly do not go far once you get in. As the Broncos showed last year and the Patriots and certainly the Seahawks before that, a team can win the Super Bowl with a super secondary.

The Giants, as the Cowboys learned, twice, the hard way, have a super secondary.

“It works hand in hand,’’ linebacker Jonathan Casillas said. “I feel like a lot of those pressures and a lot of those hits on the quarterback were coverage sacks, coverage hits. Great job by the back end. We have a ton of really skilled, really crafty, really smart defensive backs.’’

The days of receivers running free, occupying wide swaths of unoccupied territory, are gone, even if they are not forgotten (does 2015 ring a bell?). General manager Jerry Reese reconfigured the secondary by signing Janoris Jenkins and drafting Eli Apple in the first round. The coaching staff then smartly moved veteran Dominique Rodgers-Cromartie into the slot corner position, reduced his snaps to keep him healthy and fresh and — voila! — the Giants possess one of the top cornerback trios in the league. Add in second-year safety Landon Collins — a rising star in contention for Defensive Player of the Year honors — plus solid depth with Trevin Wade, veteran free-agent import Leon Hall and even undrafted rookie Andrew Adams, and there are no weak links in the defensive backfield.

Standing tall (at least defensively) at 9-4 heading into Sunday’s game against the surging Lions, the Giants are healthy and wealthy in the secondary. They are tied with the Cardinals in allowing the second-fewest passing touchdowns (13) in the NFL — the Broncos are first with only 10 touchdowns allowed through the air. The Giants own the second-best opposing passer rating (76.3) in the league, behind only the Broncos (67.7), according to Pro Football Focus.

Jenkins has been worth every penny of the $62.5 million deal he signed, locking up the opponent’s top receiver and coming out ahead in the matchup. He owns Dez Bryant. After stopping him cold (one catch for 8 yards) in the season opener, Jenkins blanketed Bryant in the rematch. Prescott targeted Bryant seven times with Jenkins on him and Bryant caught one pass — late in the fourth quarter — for 10 yards. But Jenkins knocked the ball loose, forcing a fumble that Collins recovered. It was akin to allowing a single to a batter and then picking him off first base.

“If you play defensive football the way we played defensive football last night, you’re always in the ballgame and have a chance to win,’’ Ben McAdoo said Monday.

Apple, after some rough moments early in the season, has settled in as an outstanding prospect. He played all 66 snaps against the Cowboys and again showed the range, speed and length to make it difficult to sneak the ball past him.

What do the Giants know about Prescott that the rest of the NFL does not? In two games against the Giants, Prescott has thrown 40 incomplete passes. That is staggering.

All three sacks of Prescott in the rematch were the result of excellent coverage down the field. Prescott, as a rookie, is not yet a pure NFL passer. He relies on a great running game and plenty of play-action passing options. The Giants plastered so closely with their coverage that Prescott could not make all the throws in close quarters.

“I feel like we gave him some different looks, some different personnel out there, throwing some different stuff at him,’’ Casillas said. “We blitzed him, we played some coverage, we sat back and played man to man. We didn’t let him just sit there and figure out what we were in and pick us apart.’’