LOS ANGELES: Aaron Gordon scored a last-gasp three-pointer and Nikola Jokic produced a 42-point masterpiece as the Denver Nuggets stunned the top-seeded Oklahoma City Thunder 121-119 in a dramatic NBA Western Conference semifinal series opener on Monday.

Nuggets forward Gordon drained a 25-foot effort from outside the arc with four seconds remaining to snatch victory against a Thunder lineup who had led by as many as 14 points in the third quarter at the Paycom Center in Oklahoma City.

The Thunder continued to lead by double digits for much of the fourth quarter, but saw their advantage evaporate after 18 points from Serbian star Jokic in the final frame.

The towering three-time NBA Most Valuable Player finished with 22 rebounds, six assists, two blocks and a steal in addition to his 42-point tally.

Oklahoma City were left ruing two missed free throws from forward Chet Holmgren with 10 seconds remaining with his team defending a slender 119-118 lead.

Those misses proved costly, with Denver rebounding and launching the final offensive raid that ended with Gordon’s winning three-pointer.

Denver interim coach David Adelman paid tribute to the all-round effectiveness of Gordon, who finished with 22 points and 14 rebounds.

“I’m looking at ball-handling, responsibilities, leadership — he is a Denver Nugget, the soul of our team,” Adelman said. “So cool to see him have a moment like that.”

Gordon said the Nuggets’ calmness under pressure had helped them close out the win.

“A lot of guys stepped up,” he said. “We had poise and a belief that we were going to win no matter the circumstances.”

Gordon and Jokic were backed by 21 points from Jamal Murray and 18 points from Russell Westbrook.

Shai Gilgeous-Alexander led Oklahoma City with 33 points, 10 rebounds and eight assists, with Alex Caruso scoring 20 off the bench after shooting five three-pointers.

Game 2 of the best-of-seven series takes place on Wednesday.

In the Eastern Conference semifinals, a pulsating battle in Boston saw the New York Knicks dig deep to edge past the reigning champion Celtics 108-105 after Jalen Brunson and OG Anunoby scored 29 points apiece for New York.

Brunson — the 40-point hero of New York’s series-clinching win over Detroit last week — was once again in superb form as the Knicks climbed out of a 72-52 hole in the third quarter to snatch Game 1 at the TD Garden.

Brunson’s 29 points included five-of-nine from three-point range, with Anunoby pouring in six three-pointers in his 29-point haul.

Jaylen Brown and Jayson Tatum led Boston’s scoring with 23 points apiece on a miserable shooting night for the Celtics, who missed 45 three-point attempts — the most ever missed threes in a playoff game.

“It was a great team win,” Knicks coach Tom Thibodeau said.

“We started well, then we fell into a hole and then we fought our way out and then we made tough plays down the stretch,” Thibodeau added.

Celtics coach Joe Mazzulla said lax defense in the second half cost his team dearly.

“We left some of their good shooters open,” Mazzulla said. “There’s detail stuff that we have to be better at.”

Brown, who shot only seven-of-20 from the field and made only one-of-10 attempted three-pointers, said the Celtics would not get hung up on their wayward shooting night as they prepare for game two in Boston on Wednesday.

“We had a historic night of missed three-pointers,” Brown acknowledged. “We’ll take a look and kind of see what the energy was.

“In reality you’ve got to have a short-term memory — throw it away and get ready for game two.

“We don’t have time to let stuff carry over.”