The Nets lost James Harden less than a minute into the Eastern Conference semifinals. But they never came close to losing Game 1.

Riding their vaunted offense and some surprising perimeter defense, the Nets constructed a resounding 115-107 victory over the Bucks before a raucous sellout crowd of 15,750 at Barclays Center.

After Harden limped off just 43 seconds into the game with an injured right hamstring, the rest of the Nets’ Big 3 came up huge when they were needed. Kevin Durant had 29 points and 10 rebounds, while Kyrie Irving turned in a stellar effort with 25 points, eight assists and five rebounds in 44 marathon minutes.

“We try not to be too emotional out there, but losing one of your leaders like that first play of the game, we had to regroup for a few minutes and figure out what was next,” Durant said. “But the coaching staff did a great job of moving forward and guys came in and just tried to play extremely hard. We didn’t care about anything else but playing and executing the game plan and leaving it all out there.

“We’re gonna be thinking about James. Definitely gonna call him when I leave here and see how he’s doing. … It’s a bad situation, man. I hate that it had to happen.”

Mike James — who was signed after LaMarcus Aldridge retired, but hadn’t played more than a minute since Game 2 of the first-round series against the Celtics — was summoned from the bench due to Harden’s injury. James finished with 12 points and seven rebounds in 30 minutes.

Center Blake Griffin had his second double-double of the season (18 points, 14 boards) and contributed a solid effort to help keep Bucks star Giannis Antetokounmpo (game-high 34 points) from completely wrecking the game.

Harden’s injury was a sucker punch for the Nets, but they hit back. That has been the story of their season, during which they had to use a team-record 38 different starting lineups.

“Yeah, absolutely,” Irving said. “Just in terms of the journey this year, what it’s taken for us to just continue to persevere and just be resilient. We just gotta dig deep, especially when you don’t know when some of those situations are gonna happen. Like I said, we feel for James, and all of us feel it, so just gotta pray and wish him the best and want him to get healthy.”

After the Nets — somewhat shaken by the loss of Harden — fell behind 20-9 with 6:58 left in the first quarter on a Antetokounmpo hook shot, they quickly steadied the listing ship.

Griffin provided some physicality and hustle, twice diving on the floor to save loose balls. The first one he wrestled from Bryn Forbes and Bobby Portis as the sellout crowd gave him a huge ovation. He got more cheers when he fouled out with 1:26 remaining, the crowd recognizing what he had brought.

When the Nets got within 42-39 with 9:11 in the second quarter, their defense found its footing and sparked a quick two-minute burst and eight unanswered points. With their offense, the Nets don’t need to be stellar defensively, just good enough. And Saturday, they were good enough.

The Nets held Milwaukee to 6-for-30 shooting from 3-point range, and Khris Middleton to 6-for-23 overall.

When James hit a step-back 3-pointer with 7:40 left in the first half, it gave the Nets a 47-42 lead they never surrendered.

Irving put the Nets ahead 59-48 with a running layup, and even after facing the inevitable Bucks run led by Antetokounmpo, they withstood it. The Nets took a 63-61 edge into the locker room, regrouped and padded their lead in the second half.

The Nets were clinging to an 86-80 lead with just over two minutes left in the third quarter, when Durant sparked a 12-2 run. His step-back 3-pointer padded it to 98-82 with 5.1 seconds left in the period.

They cruised to victory from there. Game 2 will be Monday at Barclays Center.

“Yeah, it’s happened to us all year. Something has happened, some sort of adversity. Someone goes down, and the next man is up,” head coach Steve Nash said. “Mike, who would’ve thought before the game he was going to play 30 minutes? Scored the ball, rebounded, made a few plays and hustled and it’s just great to see guys who haven’t been in the rotation get an opportunity to step up and play well.”