When looking for positives from the Giants’ starting offense this preseason, sometimes you have to dig pretty deep.

Take a first-quarter incompletion from Ryan Nassib to Larry Donnell on Thursday night against the Patriots. A go-nowhere play from the 37 on a possession that ended with a punt. A forgettable line on the stat sheet. But inside that snap might be the biggest glimmer the Giants take away from their 17-9 win over the Patriots at MetLife Stadium.

Victor Cruz was able to get off the line of scrimmage against press coverage by Pro Bowl cornerback Malcolm Butler and was open down the sideline. So open, in fact, that he raised his hand calling for the ball. It’s the kind of flash separation the “old Victor Cruz” gave the Giants, and what they have been hoping to see from him this summer.

“Slowly but surely, I do feel like I’m getting that sudden step back and being able to get some separation,” Cruz said after the game.

Cruz may not have caught a pass in his final preseason game — he was targeted once — but when the coaches watch tape of the game, he’s bound to catch their eye on that route. That’s apparently what they wanted, given that Cruz was the only offensive player with star power who played in the game. Eli Manning and Odell Beckham Jr. sat and watched, as did starting center Weston Richburg.

Cruz needed to prove himself a little more before the Sept. 11 opener in Dallas. That seemed to happen. “I thought he had a couple of nice releases,” coach Ben McAdoo said.

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Asked how sure he is that Cruz can be productive this season, McAdoo said: “I’m confident . . . I saw that release on our sideline, that helps. I see him in practice every day. I see the twinkle in his eye.”

“He looks like he’s feeling good, he’s ready for the season,” Beckham said of Cruz’s performance during the television broadcast of the game. “I know we’re all excited.”

Not everyone looked ready. The offensive line continued its woeful trend, unable to open holes for the running game and endangering Nassib. On one play, the backup quarterback was hit from behind — on a one-step drop! — when linebacker Barkevious Mingo shot past center Brett Jones on a blitz. The result was a backward pass that rolled out of bounds for a loss of 10 yards. Left tackle Ereck Flowers was pushed backward for a sack. Rookie running back Paul Perkins fumbled for the second time this preseason and dropped a pass. Nassib threw a pass to the New England 1 that was intercepted late in the half.

The bright side continued to be the defense. Trevin Wade, who had been marginalized since the addition of veteran cornerback Leon Hall early in camp, intercepted Tom Brady and made two nice tackles at the line of scrimmage on short passes. Rookie safety Andrew Adams forced a fumble that was recovered by Montori Hughes. Eli Apple was able to cover Julian Edelman deep. Kerry Wynn forced a fumble that was recovered by Mark Herzlich and Romeo Okwara had a sack.

Notes & quotes: WR Tavarres King likely sealed a spot on the 53-man roster when he caught a short pass for a 59-yard touchdown in the third quarter. It was his third TD in two games . . . Rookie Roger Lewis Jr. caught a 17-yard TD pass from Logan Thomas with 3:49 left in the game . . . Donnell appeared to injure his hand while making a “catch” in the second quarter. Replays showed the ball was dropped, but the play was not reviewed (it was inside the final two minutes of the half and the Patriots could not challenge) . . . RB Andre Williams did not take an offensive snap until the fourth quarter, casting doubt on his roster security . . . After the game Brady swapped jerseys with Beckham. “He’s a great player,” Brady said. “I love watching him. It’s kind of the thing to do these days.”