The boos first arrived less than three minutes into the third quarter, when a Jimmy Butler bucket prompted a 76ers timeout as the Miami Heat scored the first eight points after the break.

Some home fans began heading for the exits with less than seven minutes to play, when a Sixers turnover became a Butler transition dunk to give the Heat a 19-point lead.

And as Butler scored again inside to halt a too-little-too-late Sixers flurry, faint chants of “Let’s go Heat!” rippled through the shrinking Wells Fargo Center crowd.

The Sixers’ 2021-22 season ended after they wilted in the second half of a 99-90 defeat to the Miami Heat — which was much more lopsided than the final score indicated — Thursday night to lose their best-of-seven Eastern Conference semifinal series, four games to two.

“We just [weren’t] good enough,” All-Star center Joel Embiid said.

The top-seeded Heat took control immediately after halftime with a 19-4 run to turn a one-point margin into a comfortable advantage. Butler, the former Sixer, spearheaded the stretch by scoring 14 of his 32 points during that decisive third quarter.

The Sixers cut the deficit to 11 points on two Embiid free throws with less than two minutes remaining in the third quarter. But the Heat scored the first eight points of the fourth — including two buckets from Bam Adebayo — to push their lead to 82-63 with about 10 minutes to play.

The Sixers were poor on both ends of the floor, shooting 41.4% from the floor — 36.4% through three quarters that mattered — while allowing Miami to score 62 points in the paint. Though coach Doc Rivers pointed to poor offensive execution, the coach and leaders Embiid and Tobias Harris added that their team did not match or exceed the Heat’s physical and mental toughness.

“At times, for our group, too many things just affected us as a whole,” Harris said. “We drop our heads too much. Our body language, at times, is crappy. ... We need to be better as a collective group of holding our head and just fighting, just going right back at it. I don’t think we did a great job of that.”

With the loss, the Sixers failed to get out of the playoffs’ second round for the 12th consecutive time, dating back to 2001-02. And it ended a season that was filled with twists, tumult and triumph, from the months-long Ben Simmons holdout, to the blockbuster deadline trade for perennial All-Star James Harden, to Embiid leading the NBA in scoring for a team that tied for the second-best record in the East.

It was also a postseason run marred by Embiid’s two significant injuries following the healthiest regular season of his career.

The MVP finalist tore a ligament in his thumb in Game 3 of the Sixers’ first-round series against the Toronto Raptors, and then suffered an orbital fracture and mild concussion late in Game 6 of that series. That forced him to miss the first two games against the Heat, and to wear a mask when he returned. Though his presence gave the Sixers an emotional lift in home wins in Games 3 and 4, it did not carry over to their final two losses.

The Heat move on to face the winner of the Eastern Conference semifinal between the Boston Celtics and Milwaukee Bucks, which the Bucks lead 3-2 entering Friday’s Game 6.

Embiid labors

After an uncharacteristically subpar Game 5 performance, Embiid labored his way to 20 points on 7-of-24 shooting with 12 rebounds and two assists while playing 44 minutes in the finale of a tremendous 2021-22 season. He regularly bent over to put his hands on his knees during breaks in play, a sign of fatigue in his fourth game back after missing about a week of physical activity to nurse his orbital fracture and concussion. He also hit the deck multiple times.

“I tried to be on the floor really the whole game,” said Embiid, who confirmed that he believes he will need surgery on his thumb but not on his face. “I didn’t really want to take any breaks [with the] season on the line. So I just wanted to do whatever I could and not regret anything.”

Embiid started 2-of-7 from the floor before burying a wide-open three-pointer late in the first quarter. But he struggled to establish post presence, shooting only four free throws. He missed six of his seven shots in the third quarter before scoring two points in the final period.

And Embiid did not get consistent help from his teammates on the Sixers’ poor shooting night.

Harden’s second-half disappearance was the most glaring. After making three of his first four long-range shots and dishing out five assists before the break, he went scoreless on 0-of-2 shooting and totaled four assists and three turnovers in the second half.

“Listen, I’m not going to make this a referendum on James, OK?” Rivers said. “We just could have played better. The ball could have moved more.”

Added Harden: “We ran our offense. I felt like the ball moved, and it just didn’t get back to me.”

Tyrese Maxey, meanwhile, went 9-of-22 from the floor, including misses in 13 of his first 18 attempts, to finish with 20 points. At the end of a terrific postseason, Harris went 6-of-13 (including 3-of-8 through three quarters) and finished with 14 points and eight rebounds.

Reserve guard Shake Milton, who scored all 15 of his points in the second half, was the only spark plug.

Strus was loose

The Heat’s Max Strus challenged the theory that role players are much better at home, especially in the playoffs. He finished with 20 points, 11 rebounds and five assists.

Strus hit five of his first seven shots, including three makes from beyond the arc. That was needed when Butler missed seven consecutive first-half shots after beginning the game 3-of-3 from the floor.