ARLINGTON, Texas — The Giants traded up into the back end of the first round of the NFL draft to get DeAndre Baker, whom they considered to be the best cornerback in the entire draft. Baker’s claim to fame at Georgia: He did not allow a touchdown reception in his final two seasons.

Well, it was a forgettable NFL debut for Baker on Sunday as the Giants were routed by the Cowboys 35-17 at AT&T Stadium.

“I didn’t have the best game that I wanted to have,’’ Baker said. “Just got to bounce back and show what I can do next week.’’

Baker moved into a starting role in the summer but he did not start this game, as he missed time with a knee injury and the Giants did not want to give him a full workload. Antonio Hamilton did not get a single snap on defense last season but was given his first start, and quite likely his last start for a while. Hamilton struggled, most noticeably on a third-down reception by Randall Cobb in the second quarter. Hamilton had Cobb lined up short of the first down but did not even try to tackle him, allowing Cobb to push forward for the yards he needed on what became a Cowboys touchdown drive.

Despite his streak of not having allowed a touchdown in his final two college seasons, it didn’t take long for Baker to get indoctrinated in his NFL career.

He was beaten by Amari Cooper in the second quarter on a 21-yard touchdown reception, with Cooper putting a move on Baker to lose him before Baker recovered — a step too late.

In the third quarter, Baker badly trailed Michael Gallup cutting across the middle on what turned into a 62-yard catch and run.

“Rookie corner in the NFL, out there playing for the first time,’’ coach Pat Shurmur said. “There’s a lot to be learned.’’

It was not all on the youngsters. Tight end Jason Witten (who else?), newly out of retirement, had no trouble breaking free of safety Michael Thomas for a 4-yard scoring catch to make it 14-7.

“That’s on me,’’ Thomas said. “Eyes. Can’t happen. Discipline. Got to play disciplined. That’s on me.’’

Shurmur did not agree with the intentional grounding penalty called on Eli Manning.

“We had a crazy penalty on a ball that was thrown at the feet of Saquon [Barkley],’’ Shurmur said. “I don’t know what that was all about.’’

Barkley had a rare fumble the first time he touched the ball, a catch for 8 yards, but the Giants did not lose possession as Eli Penney pounced on the ball.

“Eli Penny saved me,’’ Barkley said.

LB Kareem Martin was forced out early in the third quarter with a knee injury and did not return.