John Wall (20 points, nine assists, six steals) and Washington win their third straight following a four-game losing streak. (Michael Dwyer/Associated Press)

Marcin Gortat crowded Boston Celtics center Jared Sullinger as he drove baseline, sized him up then slapped Sullinger’s shot right into the hands of Bradley Beal. Beal tossed the ball ahead to John Wall, who raced up the court, sucked in the defense and flipped the ball over to Trevor Ariza for a three-pointer. Ariza’s basket completed a stunning run in which the Washington Wizards turned an eight-point deficit into a five-point lead in roughly four minutes.

After the shot dropped, TD Garden fell silent. Wall glared back at his bench, marveling at the cold-blooded and methodical precision of a 14-1 rally that propelled the Wizards to an impressive 106-99 victory over the Celtics. Ariza calmly backpedaled and said he told himself, “Okay, we fought back. Now let’s not stop here. Let’s keep going, let’s keep stepping on them and let’s run away with this one.”

The team that once found a way to repeatedly fumble in crunch time, that never had enough energy to finish after climbing back from huge deficits, is suddenly making the critical plays and demoralizing opponents in their own buildings.

The Wizards (12-13) overcame an 18-point deficit to claim their third consecutive road win for the first time since April 2012.

Washington got a game-winning layup by Beal in a one-point win in New York to start the week, a huge offensive putback by Gortat and a backbreaking three-pointer by Beal in Brooklyn and a lift from Ariza and Wall in Boston after a sloppy start.

The Post Sports Live crew recalls the highlights from the year in Washington sports. (Jayne Orenstein/PostSportsLive/The Washington Post)

“We don’t let anything rattle us too much,” Ariza said after making five three-pointers and scoring a game-high 27 points. “We’re starting to learn that. We’re starting to mature as a team and when you don’t get too high or too low and just play, it’s a long game. Teams go on runs and we were down early, but we still had a lot of game left and stuck with it.”

Ariza said recently that the Wizards’ struggles to close out games would eventually make them better, that their unfamiliarity with those situations would morph into experience. Now Washington is playing with a confidence that it will make the plays that matter in the end.

That poise was evident after former Georgetown star Jeff Green made a layup to give the Celtics a 92-84 lead with a little more than six minutes remaining. Ariza started the run with a long jumper, then found backup Kevin Seraphin (13 points) for a dunk.

Wall missed his first four shots from three-point range but didn’t hesitate to pull up for a three-pointer to bring the Wizards within one. Nene replaced Seraphin and immediately tied the game with a bank shot from the left side of the rim. Wall followed by giving the Wizards their first lead at 95-93 with a pull-up jumper from 20 feet and started applauding.

“They are beginning to grow up before my eyes in terms of having perseverance that this group is starting to develop. I’m seeing it,” Coach Randy Wittman said. “To win on the road, you have to be mentally tough. Not in your own bed, you are eating terrible restaurant food, all those things.”

Wall was upset with himself for failing to deliver in losses this month against Milwaukee, Denver and Atlanta, but he was consistently coming through, especially on the defensive end against former Wizard Jordan Crawford. Wall finished with 20 points, nine assists and a season-high six steals, with two coming in the fourth quarter.

“I’m trying to learn and watch all the mistakes of the things I did wrong,” Wall said. “As long as we play as a team, I think we’re building. I think we’re figuring out how to stay humble and how to stay through the tough times, and that’s how you become a better team and a playoff team.”

Nene, with his minutes still being limited as he recovers from tendinitis in his right Achilles’ heel, contributed 13 points with eight rebounds in just 23 minutes off the bench. Nene found Gortat inside for a reverse layup late, and made all four of his free throw attempts in the fourth quarter.

“I’m in the process of coming back from injury. Maybe the next two games it’s going to be like that until I feel comfortable and I feel better to receive the same minutes I’ve been playing,” Nene said. “If that is 30 minutes or 10 minutes, I’m always going to give my best.”

Crawford (11 points, eight assists) came out fired up in his first start against the team that discarded him just 10 months ago and had seven points and four assists in the first quarter, giving his team a 16-point lead when he dribbled up the court and buried a fallaway three-pointer. The Celtics went ahead 32-14 when reserve Gerald Wallace made a layup to start the second period.

The Wizards cut the margin to 51-44 by intermission, and Wittman reminded his players they had what it took to win. “We didn’t plan to start like that, but that’s part of the business,” Gortat said after scoring 13 points with 11 rebounds and four blocks. The Celtics “punched us first. I’m just glad they didn’t get a KO in the first quarter. It’s still too early to say something, but if we’re going to continue to play like that, grow as a team, build this chemistry and build this momentum, we’re going to be able to put ourselves in a good position before the playoffs.”