Al Horford is a 17-year veteran. A five-time All-Star. A universally respected locker room leader. And now — finally, after nearly two decades in professional basketball — an NBA champion.

The Celtics’ 106-88 victory over the Dallas Mavericks at TD Garden both ended Boston’s 16-year championship drought and gave Horford his first title.

Entering Monday, only Karl Malone had played more NBA playoff games without a title than Horford’s 185, spread across stints with Atlanta, Philadelphia and Boston. The 38-year-old now can remove himself from that ignominious list.

“It’s been long,” a beaming Horford said postgame. “A lot of hard work. But I’m so proud to be part of this team and that it happened now.”

Horford’s unselfishness was a vital ingredient in Boston’s run to Banner 18. A starter throughout his career — including in his first five seasons as a Celtic — he accepted a move to the bench following the offseason additions of Jrue Holiday and Kristaps Porzingis, giving the Celtics the deepest roster in basketball.

Then, when Porzingis went down with a calf injury four games into the playoffs, Horford stepped back into his familiar old role and delivered some of the most resonant performances of the postseason.

Horford hit six 3-pointers as part of a 22-point, 15-rebound, four-block tour de force in the second-round closeout win over Cleveland, then sank seven threes to help the Celtics rally past Indiana in Game 3 of the Eastern Conference finals.

In all 16 of its playoff victories, Boston scored more points than it allowed with Horford on the floor. He started the final 15 games, with a limited Porzingis coming off the bench three times in the Finals.

Horford played 32 minutes in Monday’s clincher, tallying nine points, nine rebounds, two assists and one steal.

“I can’t believe it,” he said. “I still can’t believe it. We did it, we’re here, but I can’t believe it. This is just how I pictured it, here at the Garden with our fans, everybody together. This is just how I saw it eight years ago.”

As the on-court trophy ceremony wound down, Horford’s father, Tito, himself an ex-NBA player, walked toward the Celtics’ family area in the bowels of TD Garden, extended both arms above his head and bellowed: “Yes! We got it!”

A happy night for the Horford family indeed.

Porzingis guts it out

Before Game 5, Porzingis sweat through an extensive on-court workout in front of the Celtics’ medical staff.

That staff, which had ruled him out for Game 3 and allowed him to be available in a highly limited role for Game 4, had a different ruling Monday.

Porzingis was good to go. And that he was.

Porzingis finished with five points on 2-of-4 shooting and added a rebound during a title-clinching Game 5 win Monday night. He finished plus-eight over 16 minutes.

Porzingis was not 100% healthy, but he provided enough of a spark off the bench to help extend Boston’s lead in the first half.  The Celtics never trailed after halftime.

Porzingis scored all of his points by posting up Mavericks guards, first drawing a foul that led to a 1-of-2 showing at the foul line late in the first quarter. Later, early in the second quarter, he made a mid-range basket over Kyrie Irving.

Porzingis missed Boston’s last two games with a dislocated tendon in his left ankle/foot caused by torn connective tissue he suffered in Game 2. Before Sunday’s practice, Celtics backup Xavier Tillman made it sound unlikely that Porzingis would play, saying he still looked “very uncomfortable” in practice.

But asked post-game about the possibility of sitting in Game 5, Porzingis had a different answer.

“How could I?”

Mavericks coach Jason Kidd made it clear pregame that Dallas would test Porzingis’ hurt ankle on defense.

“We’ll see how he moves. I think healthy or not healthy — healthy, we’re still going to check to see how he moves,” he said. “So nothing changes there.”

The Mavs drew Porzingis into the action on his first four defensive possessions, all of which yielded open 3-point looks. But the big man remained steady, found a rhythm and emerged an NBA champion.

Pritchard does it again

Welcome to Celtics immortality, Payton Pritchard.

After not seeing the floor for nearly the entire first half as Mazzulla tightened his rotation, Pritchard checked in with four seconds remaining before halftime and did what he does best: bury an incredible long-range shot at the buzzer.

This was his finest work yet. After Luka Doncic bricked a free throw and Horford grabbed the rebound, Pritchard received a pass, took a running start and let one fly from beyond halfcourt. Bang.

His 43-foot heave gave the Celtics a 67-46 halftime lead, and the Mavericks never recovered.

Pritchard went just 3-for-16 on 3-point attempts in the series and totaled 17 points across the five games, but those stats will be quickly forgotten. What Celtics fans will remember are his two unlikely buzzer-beaters: one to close out the first quarter in Game 2 and the second Monday night.

“Bro I hate this dude,” Mavericks fan Patrick Mahomes posted on X after Pritchard’s latest dagger.

Fellow bench shooter Sam Hauser also made a sizable impact in his 16 minutes, finishing with eight points, four rebounds, one assist and one steal.

Off the rim

Among the notable attendees Monday night: Grant Williams, who owns the rare distinction of having been traded by both NBA Finals participants within the last 12 months. Ex-Celtic and Maverick Jason Terry also was in the house, as were Bruins captain Brad Marchand and Patriots rookie quarterback Drake Maye.