The Nets got back Kevin Durant. But they didn’t get Kyrie Irving — or a win.

The Nets wasted Durant’s strong return from a weeklong quarantine, and squandered a big lead in a 129-116 loss to Oklahoma City at Barclays Center.

Having missed the prior three games due to COVID-19 contact tracing, Durant had 36 points, 11 rebounds and four assists. With Irving missing a third straight for personal reasons, Caris LeVert added 21 points and six assists.

But with the Nets’ sieve-like defense, it wasn’t enough. They blew a 15-point cushion in the second quarter and five-point lead in the third.

Brooklyn surrendered a 25-7 run to end the period, allowing 54.4 percent shooting. And it was the 66 points in the paint — and 72 surrendered in the second half — that had even perpetually positive coach Steve Nash seeing red.

“In the second quarter it was turnovers. We were kicking the ball all over the gym. Up 15, lack of focus, it gets them right back in the game,” Nash said. “It’s just pride. No matter what defense you’re in, you got to sit down and guard someone, and we didn’t guard.

“You can get beat, you can have a hard time guarding someone; but I didn’t sense the pride. I didn’t sense the competitive fire in the second half. I thought it was a lack of respect. We’ve just got to learn from this and get better.”

It’s become a reoccuring theme with these Nets, and a disturbing one. Faced with teams that entered Sunday with winning records, they’ve risen to the challenge and gone 4-0. Against clubs .500 and under? They’ve played down and gone 1-6.

“It might be. I hope it’s not,” Nash said. “This is going to be a very unique season. Everyone’s getting beat by everybody, and it’s really important that we respect our opponents. We got up 15, and played like we felt the game was over. That’s just got to change. We’ve got to learn from it. We’ve got to toughen up and show a little pride.”

The Nets were up 44-29 in the second quarter after Taurean Prince’s 3, and still led 74-69 with 6:52 in the third. But that’s when they allowed a 25-7 run to lose control of the game. They shot just 3 of 11 with four turnovers, but even worse they couldn’t guard one-on-one or stay in front of their men.

“We just got to get consistent at it. We’ve played some great defensive games this past week when I was out, and throughout the season we’ve been up and down on that side of the ball,” said Durant, adding, “You’ve got to give credit to these other teams that’s coming in here and playing with a sense of urgency to start.”

The Nets didn’t play with one until it was too late.

Shai Gilgeous-Alexander (31 points) helped put the Nets in a 94-81 hole after three, and Hamidou Diallo (25) threw down a baseline dunk to open the fourth. The Nets spent the rest of the night chasing.

With rebounding having been a weakness, Nash started his biggest lineup with Jeff Green at small forward and Joe Harris at off-guard. It shored up the boards, but left the Nets vulnerable on the perimeter on switches.

“That may have contributed to it for sure,” said LeVert. “It’s Game 11, 12. It’s getting up there. We can’t keep saying the same things. So that may have contributed to it — the bigger lineup — but we still have to play better defense.

“We couldn’t keep the ball in front of us. They were getting to the rim and getting easy kick-out 3s, so we have to figure that out. [Allowing] 129, that’s unacceptable. We can’t allow that many points and expect to win.”

The Nets will have a chance to get it right at home on Tuesday against Denver. And even with Irving’s status undecided, they do have Durant.

“I definitely would’ve loved to be out there with my teammates, but COVID just put us under these circumstances,” Durant said. “It’s something we knew coming into the season that may happen. I wasn’t too upset about it, I’m glad I’m back playing though.”