From the start of the season to now, the Nets defense has gone from sieve to stout.

On Sunday, it was smothering.

The Nets pulled away for a 96-81 rout of the Raptors before a sellout crowd of 17,548 at Barclays Center. And it wasn’t with potent offense but stifling work on the other end of the floor down the stretch.

The Nets (8-19) allowed their fewest points of the season, bettering the 82 they’d conceded in a 45-point beating of the Bucks a week earlier. It’s the first time they’ve held foes to 82 points or fewer multiple times in a season since 2018-19.

Down by two in the fourth quarter, the Nets seized control with a 24-6 run. And more and more, solid defense isn’t an exception but an expectation.

“Just doing what we do better,” Nic Claxton said. “And our defense has been pretty solid this past month. It’s been really good. So we’ve just got to keep taking steps in the right direction. But we’ve been doing a really good job guarding. We’ve got a lot of switchable defenders. We’ve still got a lot of areas we can get better, but we’ve got to just keep going.”

Indeed, the past month has been as impressive as it has been unexpected.

The tanking Nets have held opponents to just 102.3 points per game so far in December, the fewest in the NBA, surpassing OKC. Considering the embarrassing way they opened this season — compiling a league-worst 128.5 defensive rating in an 0-7 start — the turnaround is shocking.

“We didn’t start [the season] well at all defensively. It was very poor. We didn’t buy into a lot of things,” Nets head coach Jordi Fernández said. “Obviously, we’ve evolved and made some adjustments.

“But now, it feels like we have a good rhythm with our physicality, with our communication, getting multiple stops in a row, making winning plays. We’re building our defensive identity. And I give credit to the coaches to structure the work and to the players to do the work, and then put it out there on the court.”

The Nets matched their best defensive first quarter (18 points) and had their best defensive half (39 points) of the season. Then they went out and closed the deal, holding Toronto to 37.2 percent shooting and 10-of-36 from deep.

Part of that may well be the Raptors not getting in until after 4 a.m. But the Nets didn’t care, pouncing on their weary foes.

Trailing 71-69 with 10:10 to go after a bucket by Immanuel Quickley (17 points, 10 assists), the Nets mounted a 24-6 blitz. They held the Raptors to 1-of-10 shooting with a turnover during that run and hit 10-of-13 themselves to seize the game.

Michael Porter Jr. had a game-high 24 points on 4-of-8 from deep, with 11 rebounds and five assists. Noah Clowney added 19 points, nine boards and two blocks and rookie Egor Dëmin had 16 points, five rebounds and two steals and sank 4-of-8 from behind the arc.

“We lost a little focus in the third quarter. So for us, it was really important to get back to the rhythm and to get back to hustling every single possession, offense and defense,” Dëmin said. “We got this feeling as we’d been playing the first two quarters with. So that’s what helped us. We’ve been dialed in on defense.”

The Nets were down by a bucket in the final period but squeezed the life out of the fatigued Raptors. They outscored Toronto 29-16 in that fourth quarter, when they allowed just 27.3 percent shooting and 0-of-9 from deep.

“I think us punching back. They took the lead. It was a collective effort,” Fernández said. “Noah made unbelievable plays, winning plays at the rim, whether it was to get a block or to go vertical. And then Egor’s 3s were huge. And then from there, everybody contributed to win in that fourth quarter.”