CHICAGO — The longest winning streak in the NBA this season came to a crashing halt Wednesday, as the Nets were beaten 121-112 by the Bulls at the United Center.

After a dozen straight victories, the Nets finally tasted defeat. They hadn’t lost since Dec. 4 against the Celtics, and after nothing but victory for a solid month, Brooklyn was bested. Now starts the process of getting back to work to forge another string of victories.

Kevin Durant poured in a game-high 44 points, but the Nets were profligate, squandering his performance — and a golden opportunity to pull even with Boston atop the Eastern Conference. It was the defense that let them down, unable to slow the Bulls’ potent midrange game.

Chicago had snapped the Celtics’ long winning streak, and on Wednesday broke the longest run since the Suns’ 18-game streak last season.

The last time the Nets saw Chicago was on Nov. 1 in Jacque Vaughn’s first game replacing fired Steve Nash as the team’s coach. Kyrie Irving — who had been mired in a firestorm of his own making, after promoting an anti-Semitic movie — had been horrible that night, with a season-low four points on 2 of 12 shooting with three turnovers.

Wednesday he had 25 points, while Seth Curry added 22 off the bench. But after letting Chicago shoot 53.1 percent overall and put all five starters in double figures, it didn’t matter.

“If you want to rewind, you’ve got to rewind and understand the circumstances at that time and what was happening to the organization and where I was,” Vaughn said. “I was just filling in that night. I was just doing my responsibility as an assistant coach. That’s what I was asked to do.”

Defense was in short supply Wednesday, at least from the Nets. They allowed misprint-like 73.9 percent shooting in the first quarter, the Bulls hitting 4 of 7 from 3-point range. It was only the Durant-led offense that kept them in striking distance, down just 40-33.

Chicago’s midrange game and the interior power of Nikola Vucevic (21 points, 13 rebounds) gave the defense fits. And they 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 Bulls bench. They still trailed by 10 at the break, however, after allowing 57.8 percent shooting.

The Nets 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 driving layup. His free throw made it 71-68 three minutes in, and it was still three going into the fourth.

But Brooklyn got no closer.