LONDON — Like an alarm clock that awoke NFL fans back home about their potential, the Giants shattered the calm and predictability of a sleepy Sunday morning in the States with one of their biggest wins in years.

It was a game in which they were momentarily without Saquon Barkley, without a fully healthy or mobile Daniel Jones, without the first three cornerbacks on their projected depth chart and, for most of the contest, without the lead against the best quarterback they will face all season.

None of it mattered, though, as the grittiness and self-belief they have demonstrated at many points this season was put on display for an international audience. The Giants beat the Packers, 27-22, at Tottenham Hotspur Stadium, overcoming a 10-point halftime deficit and shutting out Aaron Rodgers in the second half.

In a stadium that rocked like Lambeau, the Giants entered to loud boos and walked off as something no one outside their locker room had them pegged as a month ago.

Contenders.

Rookie linebacker Kayvon Thibodeaux was asked what this win means.

“It’s putting the world on notice,” he said.

The whole world indeed. The Giants declared more about themselves on Sunday than they did going through customs on the way home.

“The guys just kept playing,” coach Brian Daboll said. “We don’t want to flinch. We just want to keep playing when something bad happens. It’s easy to say. It’s hard to do.”

The win improved the Giants (4-1) to 3-0 in London. Each previous time they have played overseas, they have advanced to the playoffs.

They certainly left England on that kind of a trajectory again. Not that they ever doubted it themselves.

“Our reality is that we are for real every time we step on the field,” left tackle Andrew Thomas said.

That kind of boast is a lot easier to believe now.

It was hard to imagine late in the third quarter when with the Giants trailing 20-13, Barkley was tackled awkwardly and his shoulder was driven into the ground after he caught a short pass. He headed to the blue medical tent and then the locker room, and it certainly appeared as if the team’s aspirations left the field with him.

Instead, the Giants embarked on a 15-play, 91-yard drive for the tying touchdown. Gary Brightwell, playing only because of Barkley’s injury, scored on a 2-yard run with 10:08 left. His plunge capped a drive that included a third-down conversion pass to tight end Daniel Bellinger, three scrambles by a clearly limited Jones, a 16-yard pass to practice-squadder Marcus Johnson (in which Jones rolled to his right for the first time all game) and a third-down pass to David Sills.

The Giants then forced a three-and-out — Rodgers attempted two deep passes against backup cornerbacks Fabian Moreau and Nick McCloud that fell incomplete — to give the ball back to Jones.

And . . . to Barkley.

The running back returned to the field with some extra padding on his shoulder, perhaps to protect the chip that has been there all season. While the game waited for the commercial break to end, Barkley was on the field dancing to “Sweet Caroline” the way he said he used to back at Penn State.

On his second play back, Barkley caught a short pass and took it 40 yards. Five snaps later, he took a direct snap in a Wildcat formation and sprinted to the right pylon from 2 yards out to give the Giants a 27-20 lead with 6:08 remaining.

That was plenty of time for Rodgers to march the Packers into scoring position, and he reached the Giants’ 7 with 1:11 remaining.

On third down from the 7, he tried to throw right, but his pass hit Thibodeaux in the facemask and ricocheted high in the air (it was nearly intercepted by Tae Crowder). That set up the critical fourth down.

Xavier McKinney and Julian Love came screaming off the left edge in defensive coordinator Wink Martindale’s version of the London Blitz, forcing Rodgers to throw off schedule. McKinney batted the pass in the air and the ball fell to the ground incomplete with 1:02 remaining to virtually seal the victory.

Virtually, because after the Giants took an intentional safety with 10 seconds left, Rodgers had one last chance to win the game. The king of desperation passes — including a huge one at the end of the first half against the Giants in the 2016 playoff game — never got a chance to launch the ball more than half the length of the field, though. Linebacker Jihad Ward pressured Rodgers forward and Oshane Ximines sacked him, forcing a fumble recovered by Green Bay, to officially end the game.

Barkley finished with 106 all-purpose yards, 70 of them rushing. Jones completed 21 of 27 passes for 217 yards and ran for 37 on 10 carries. Rodgers was 18-for-24 for 147 yards and two touchdowns in the first half. He was 7-for-15 for 75 yards with no touchdowns and sacked twice in the second half.

“The thing that has changed is we are finding ways to win games,” Barkley said. “There have been a lot of times in my career we’ve been in situations like we have been here in the first couple of games and we always wound up on the wrong side of it.”

Now it’s different. The Giants return home different, too. At least from an outside perspective.

“I don’t give a damn what they say,” McKinney said of the outside doubters, a crowd that is dwindling with each passing victory. “We knew from the jump in OTAs what our goal was, what our mission was. We knew what we wanted to be as a team. I think we’re still growing, but I think we’re on a good track to be there.

“We just have to keep winning.”

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