CHICAGO — The longest winning streak in the league in more than a year is over. After nothing but victory for a month, the Nets tasted defeat.

It tasted like wasted opportunity.

Brooklyn flushed a brilliant night from Kevin Durant and squandered a chance to climb into first place in the East as the Nets fell 121-112 to the Bulls on Wednesday night before a sellout crowd of 21,418 at the United Center.

It snapped a 12-game streak and was the Nets’ first loss since Dec. 4 against Boston, the only team ahead of them in the standings. The Nets (25-13) could’ve pulled into a flat-footed tie, but now find themselves a game behind the Celtics and in third after Milwaukee’s victory.

Durant poured in a game-high 44 points, but the profligate Nets threw away his prodigious outing. They allowed 53.1 percent shooting and watched the Bulls put six players in double figures.

“It was on us,” Royce O’Neale told The Post. “We had a couple of letdowns, mistakes on the defensive end that we could’ve avoided and that they took advantage of. … So it’s just learning from it and being more aggressive and more alert.”

Brooklyn conceded 73.9 percent shooting in the first quarter and trailed by 18 in the second, never getting closer than three the rest of a night spent chasing.

Chasing in vain.

“We could not get over the hump, and a big part of it was we were playing catch-up the whole night. The 40-point first quarter set the tone,” coach Jacque Vaughn said. “So tip your hat to them; they came to play. They were pretty desperate to get a win, and we needed that same desperation.”

In some ways, victory defeated the Nets. They’d vaulted from eighth in the East up to just a half game back, but didn’t come out with the same focus on Wednesday. And Durant agreed that they’d simply dug a hole defensively they couldn’t climb out of.

“Oh yeah, I feel the same way,” Durant said. “I feel like in some of our coverages, we were playing catch-up a bit.

“Against this team, you’ve got three elite scores from all angles on the floor. You got to be there, you’ve got to do your work early [in the possession] and you’ve got to just be there on the catch. So I felt like a lot of times we chased them a bit. And that was just consistent throughout the whole game, us just playing from behind.”

Kyrie Irving had 25 points, while Seth Curry added 22 off the bench. But the way they defended early, it didn’t matter.

Brooklyn held DeMar DeRozan and Zach LaVine to a combined 35 points on an aggregate 8-for-31 shooting. But Patrick Williams had 22 and Nikola Vucevic added 21 and 13 boards, as well as warping the Nets’ defense with his power inside.

It was only the Durant-led offense that kept them in striking distance, down just 40-33.

Chicago’s midrange game gave the defense fits. And the Nets imploded altogether over the rest of the first quarter and early part of the second.

Brooklyn got diced up, falling behind 64-46 with 3:47 left in the half on a driving layup by former Nets point guard Goran Dragic.

Durant clearly decided to try to take over. He had every Brooklyn point in a 13-5 run, along with two steals, two blocks and a glare at the Chicago bench. The Nets still trailed by 10 at the break.

They pulled within three with a 26-19 third quarter.

The first six points off the half pulled the Nets within 69-65 on an Irving layup. It was three going into the fourth, and they got within 98-95 on Irving’s driving layup with 9:29 to play, but no closer.

“To be honest with you, 40 points in the first quarter is a lot, especially when you’re playing the Bulls who are trying to find their rhythm over their last few games,” Irving said. “We put ourselves in a hole in that first and second quarter coming into halftime.

“Obviously, KD is special but he can only do so much on his own. We’ve been talking about just helping him out and [this] was one of those nights where we just didn’t make enough shots on the perimeter.”