Instant analysis: Celtics overtaken by Heat after dominant third quarter, lose Game 1 of Eastern Conference finals

Jayson Tatum of the Celtics was grabbed by the Heat’s Jimmy Butler as he drove to the hoop during the first quarter of Game 1.Jim Davis/Globe Staff

After surviving a pair of elimination games and defeating the 76ers in the last round, the Celtics returned to TD Garden with a clean slate against a seemingly overmatched opponent. But the Heat, who needed a fourth-quarter comeback in the second play-in game just to reach the playoffs, have been unbothered by their underdog status for weeks.

And on Wednesday, eighth-seeded Miami seized control with a dominant third quarter and then forced the Celtics to unravel down the stretch, as the Heat grabbed a 123-116 win to take a 1-0 lead in the Eastern Conference finals.

Jimmy Butler had 35 points to lead the Heat, who shot 54.1 percent from the field and 51.6 percent from the 3-point line. Jayson Tatum led the Celtics with 30 points but committed three critical fourth-quarter turnovers.

After the Heat outscored the Celtics, 46-25, in the third quarter to take a 103-91 lead to the fourth, the Celtics needed just 93 seconds to unspool a 7-0 run. But the surge briefly stalled there, with Butler’s pull-up jumpers keeping Boston at bay.

The Heat then hit their first cold spell of the game, going more than three minutes without a point. But the Celtics were unable to take advantage, undone by one miscue after another. Al Horford and Tatum threw the ball away, and Tatum then committed consecutive travels before Butler rolled in a 3-pointer with 1:02 left that made it 120-110.

Observations from the game:

▪ The start of the game rekindled a few concerning aspects of the last series for the Celtics. Jayson Tatum missed a pair of good looks inside and Horford missed an open 3-pointer. And at the other end, Butler looked rejuvenated after having a mediocre series against the Knicks. He did well getting Robert Williams into space, mixing quick mid-range pull-ups with strong drives to the hoop. On another play, he pulled Williams to the perimeter, attacked, and kicked the ball to Caleb Martin, who hit an open 3-pointer.

But after his 12-point opening quarter, Butler started the second on the bench and was quiet after his return, hitting just 1 of 3 field goals. It was no coincidence that the Celtics roared to a double-digit lead during this time.

▪ Robert Williams remained in the starting lineup along with Horford, and he was a force on offense during the first half, particularly when Boston’s offense was scuffling a bit. In the first half, Williams registered four offensive rebounds and was 5 for 5 from the field, with each basket a layup or dunk. He seemed pleased to no longer see the 76ers’ massive 7-foot-1-inch center, Joel Embiid, patrolling the paint.

▪ The Heat shot 53.7 percent from the field and 46.7 percent from the 3-point line in the first half, and trailed, 66-57, anyway. That’s not very encouraging for their hopes in this series, because they are not a dynamic offensive team in the first place. Their 11 turnovers and inability to keep the Celtics off the offensive glass were particularly damaging.

▪ Marcus Smart’s supporters and critics must have rejoiced together following his sparkling first half. Smart attempted just one shot — good news for the critics — but had the offense running so smoothly at all times. He continued to push the pace after made baskets, slid in a few nifty backdoor paces, and ended the half with a sizzling lookaway alley-oop to Williams. Smart had 10 assists and one turnover before the break.

▪ Tatum picked up his second foul early in the second quarter and seemed understandably aware of this over the rest of the first half. He either let Heat players go past him, or softly contested their jumpers. It felt like Miami should have done more to press the issue.

▪ Celtics coach Joe Mazzulla returned to an eight-man first-half rotation, with a slightly surprising twist. Point guard Payton Pritchard got the call over Grant Williams and Sam Hauser. Pritchard has mostly been out of the rotation this season and Mazzulla generally turns to him when the team’s energy is in need of a jolt. But this chance seemed like part of the regular plan. He missed his only shot during his first five-minute stint, without an assist or rebound. He got another chance in the third and early fourth and applied some good ball pressure, at least.

▪ Mazzulla took plenty of criticism earlier this season for being reluctant to take timeouts. He’d mostly moved past the habit that drove fans crazy as the season progressed, but there it was again in the third quarter Wednesday. The Heat started the second half with a 13-1 run, with several baskets coming on transition attempts that usually draw Mazzulla’s ire. During the surge, fans could even be heard yelling to him to call a timeout. But basket after basket he resisted, until a Butler 3-point play that gave the Heat a 79-78 lead with 6:28 left led to a TV timeout.

▪ The timeout isn’t just about stopping the run; it’s about denting the Heat’s confidence. By this point, they were back in the game and feeling great, and it turned into a waterfall. During the third quarter the Heat registered 10 second-chance points, 9 fast-break points, and shot a blistering 65.4 percent from the field. There were some boos when they took a 103-91 lead to the fourth.