Two years ago, when Steve Spagnuolo returned to the Giants as defensive coordinator, he had to teach the players a new system.

Last year, the system was the same but the players were different. Again, the basics had to be taught.

Now, as he enters the third year of his stint with the team, Spags would seem to have it all. The scheme has been in place and the players, for the most part, are back. Only one starter from last year no longer is on the roster — defensive tackle Johnathan Hankins signed with the Colts — and most of the key contributors beyond the 10 starters have returned.

Coming off a season in which the defense essentially carried the team to the playoffs, Spagnuolo made it clear what he wants to see in 2017.

“The goal here,” he said on Friday, “is to pick up where we left off.”

That, of course, is not as easy as it seems. Yes, the players and playbook are mostly the same. But as last year’s floundering offense showed, it can be as difficult to build on success as it is to reverse failure.

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“The challenge is to keep them hungry,” Spagnuolo said. “I’d like to start better. It was kind of slow, if I can remember back to all the games . . . We won the two games coming out of the blocks, but I would have liked to have played better defense. And then we came on.”

Spagnuolo said the key will be not to get “hung up” on the success of 2016.

“At this time last year, everybody was asking: How do you overcome how bad it was?” he said of being the worst-ranked defense in the NFL in 2015. “You don’t even think about it. You move on. You do the same thing when you do real well. But it will be a challenge.”