DALLAS >> Coach Jason Kidd had a simple explanation for why his Dallas Mavericks players brought their “A” game tonight.

“It was this or we go on vacation,” Kidd said.

Vacation plans have been put on hold as the Mavericks responded in impressive fashion in a win-or-go-home situation, routing the Boston Celtics 122-84 in Game 4 of the NBA Finals.

Luka Doncic scored 25 of his 29 points in the first half and Kyrie Irving added 21 points while helping the Mavericks avoid a sweep.

The scene shifts back to Boston for Game 5 on Monday as the Celtics will look to close it out at home. However, Dallas showed life today after Boston was the dominant team while winning the first three games of the best-of-seven series.

The script flipped in Game 4. Doncic and the Mavericks got off to a fast start and didn’t look back. Doncic started a 10-0 spurt in the first quarter with a floater and closed it with a driving layup as Dallas took a 25-14 lead with 3:19 left in the period. That early run was a sign of things to come.

“We were locked in, especially on the defensive end,” Doncic said. “We played with pace. It helped (my teammates). I’m here to help them in every way I can. We just got to play like that.”

Dallas had a 34-21 lead by the end of the first quarter, scoring the final six points on 3-pointers by Irving and P.J. Washington.

The Mavericks kept pouring it on. They doubled up the Celtics 50-25 on a layup by Irving at the 5:16 mark of the second quarter. To close the half, Maxi Kleber drilled a corner 3-pointer off an assist by Doncic. That gave Dallas a 61-35 lead at the break.

The Mavericks shot 52.3 percent from the field compared to the Celtics’ 29.7 percent in the opening half. Dallas also won the rebounding battle 29-13 over the opening 24 minutes.

“They came out desperate and I think they punched us in the mouth,” Celtics guard Jrue Holiday said, “and we couldn’t kind of recover the way we wanted to.”

Dallas turned it into a full-on rout in the second half, leading by as many as 48, taking a 115-67 lead on a 3-pointer by Jaden Hardy with 5:58 left in the game.

The Mavericks reached the 100-point mark several minutes before that on a 3-pointer by Tim Hardaway Jr. Dallas didn’t reach the 100-point mark in any of the first three games against Boston.

Hardaway finished with 15 points on 5-of-7 shooting from 3-point range. All five of his treys were made during a 2:39 stretch in the fourth quarter.

The Mavericks’ 38-point final margin of victory was the third largest in NBA Finals history. The Chicago Bulls beat the Utah Jazz by 42 points in Game 3 in 1998, and the Celtics crushed the Los Angeles Lakers by 39 in Game 6 in 2008.

“It’s real simple. We don’t have to complicate this. This isn’t surgery,” Kidd said. “Our group was ready to go. They were ready to celebrate. We made a stand. We were desperate. We’ve got to continue to keep playing that way, understand they’re trying to find a way to close the door.

“The hardest thing in this league is to close the door when you have a group that has nothing to lose. Tonight, you saw that.”

For Boston, it was a letdown for a team that remains in control of the Finals. NBA teams are 156-0 when taking a 3-0 lead in a best-of-seven series. The loss snapped a 10-game winning streak for the Celtics, who dropped to 7-1 on the road in the playoffs.

The Celtics were led by Jayson Tatum’s 15 points. Sam Hauser added 14 points, and Payton Pritchard had 11.

“Preparation doesn’t guarantee an automatic success,” Boston coach Joe Mazzulla said. “I thought we had a great process. I thought we had a great shootaround. Thought we had a great film session (Thursday). I thought the guys came out with the right intentions. I just didn’t think it went our way. I thought Dallas outplayed us. They just played harder.

“At the end of the day, we have to just maintain our process and get ready for Game 5.”