What happened?

Easy question. But a difficult and painful one Monday night at Target Center.

For two quarters the Timberwolves gave as much as they got, the sellout crowd of 18,978 was amped almost beyond recognition about a playoff Game 4 that was a one-point affair after 24 minutes.

Then, boom.

In just a few minutes the Wolves went from being in position to tie the best-of-seven series at two games each to trying to explain how the Rockets managed to score 50 points in 12 minutes of third-quarter play.

What happened?

“We came out lackadaisical,” said Jimmy Butler said. “On both ends of the court. We didn’t take anything away from them. They got every shot they wanted. Layup, three, free throw line. When that happens, they score 50 points in a quarter.”

That the Rockets did. After shooting 38 percent in the first quarter, the Rockets hit 14 of 23 in the third, including nine of 13 three-pointers. MVP candidate James Harden had scored 12 points on 4-for-14 shooting at halftime, which ended with the Rockets up a point, 50-49. That included going 2-for-7 from three. In the third quarter he hit seven of 10 shots, three of four three-pointers, all five free throws and scored 22 of those 50 points.

Boom.

“Fifty points in a quarter is a lot of points,” Butler said. “That can’t happen. That’s the game, in itself.”

It’s only happened once before. The Lakers scored 51 points in the fourth quarter of a playoff loss to Detroit back on March 31, 1962. Until then that was the only time an NBA team had scored 50 points in a playoff quarter.

Until Monday.

The Rockets didn’t score on their first third-quarter possession, but they scored on their next 11. Harden had 16 points as the Rockets started the third on a 25-5 run to push their lead to 21 points. It started with a finger roll, then three free throws when Taj Gibson fouled him on a three-point attempt. Then he hit a step-back 12-footer, a layup, a three-pointer, and another layup. His two free throws with 6:13 left in the quarter made it 75-54.

He wasn’t alone. Chris Paul scored 15 points in the quarter. Four Rockets players hit a three-pointer in the quarter, with the Wolves too often going under the screen than over.

‘‘They did a good job of making shots,” Wolves guard Jeff Teague said. “And when they made shots, their energy went up.”

The most surprising thing might have been how quickly it all happened. The Wolves had played some pretty good defense through three games in the series. In the first half Minnesota did a good job of staying in front of Harden.

But it all went south pretty quickly.

“C’mon now, he’s the MVP,” Derrick Rose said of Harden. “He had everything working. He was sizing up the rim. The floaters got his three-pointer going. I was sitting on the bench watching it. To see how it played out there in the third …”

As Wolves coach Tom Thibodeau has said many times, you can’t let up on the Rockets. Let the intensity lag for just a few moments and it can mean trouble.

“This is a very explosive team,” he said. “We’ve had two really bad quarters. You can’t do that against them.”

He was talking about Houston’s 37-17 second quarter in Game 2, and then what happened Monday.

“It’s disappointing we didn’t give our fans what they wanted to see,” Karl-Anthony Towns said. “They brought the energy tonight. We didn’t bring as much as we needed to.”