Celtics go cold while Suns warm to task and prevail at TD Garden

As Celtics teammate Jayson Tatum stood at the ready to help, Al Horford battles for the ball with the Suns' Torrey Craig.Barry Chin/Globe Staff

On most nights, a comeback from a 20-point deficit will cause TD Garden to rumble and shake, with high-energy plays by the Celtics inevitably making an opponent wilt. But as Boston clawed out of this deep hole against the Suns on Friday, it all felt arduous and temporary. It was more of a walk than a run, and even when the Celtics pulled within one early in the fourth quarter, it was unclear whether their effort would be sufficient.

In this case, the undermanned Suns regained control with a 14-2 burst and ultimately grabbed a 106-94 win. Two nights after pulverizing the Nets in the building, this loss felt like a setback.

“We just didn’t have the enthusiasm tonight,” forward Jaylen Brown said. “Just kind of going through the motions as a unit.”

The Suns were missing four of their top seven scorers, including star guard Devin Booker. Boston had its entire roster available other than guard Marcus Smart, but his absence continues to be significant.

Smart on Friday missed his sixth consecutive game because of a sprained right ankle. In addition to being the reigning Defensive Player of the Year, he conducts Boston’s offense. The Celtics failed to reach the 100-point mark just twice in their first 47 games, but they have now fallen short of the mark in three of six without Smart. They are also just 2-4 during this stretch, with one win coming thanks to a missed foul call on Jayson Tatum in the final minutes of regulation in last Saturday’s overtime win over the Lakers.

“Marcus brings energy to the game,” Brown said. “He brings pace to the game. He gets us easier shots, easier looks for our guys. And defensively, he adds that tenaciousness that gets us going, picks us up in games like this.”

Boston’s All-Star duo of Brown and Tatum should have been enough to get past this shorthanded Suns squad, however. But Tatum, whose MVP hopes have dimmed in recent weeks, was just 3 for 15 from the field and finished with 20 points, more than 10 below his average.

Brown, who was named an All-Star reserve Thursday night, had a game-high 27 points. But the Celtics made just 38.7 percent of their shots and 26.3 percent of their 3-pointers, and they committed 14 turnovers.

“I thought we had some solid looks for the majority of the game,” Celtics coach Joe Mazzulla said. “But I just thought we were inconsistent in our detail.”

The Celtics (37-16) remain in first place in the Eastern Conference, but this recent slump has left them just one game ahead of the Bucks (35-17) and 76ers (34-17) in the loss column. Philadelphia comes to TD Garden Wednesday.

Boston has generally fared well in spotlight games this season, however. The struggles have come on slightly puzzling nights such as this one, when the Celtics are expected to coast.

On Dec. 7, the Celtics roared to a 27-point win in Phoenix against a Suns team that was then at the top of the Western Conference. It was Boston’s loudest proclamation this season that it should be viewed as a true title favorite.

The rematch in Boston had less buzz. The Suns have fallen into the middle of the pack in the West, and they are not whole. When Phoenix went 4 minutes, 35 seconds without scoring a point at the start on Friday, its deficiencies appeared obvious.

The Celtics were unable to take advantage. Phoenix led, 24-20, at the start of the second quarter. The ageless guard Chris Paul scored the last eight points of the Suns’ 29-13 run that gave them a 53-33 lead with 3:55 left.

Over the rest of the half and the first four minutes of the third quarter, Phoenix mustered just two field goals, though, as the Celtics inched closer by consistently getting to the free-throw line.

At the start of the fourth quarter guard Malcolm Brogdon took a short jumper that could have put Boston in front. But Brogdon missed, and the Suns regained control with a 14-2 run that was capped by a Dario Saric 3-pointer that made it 88-75.

“That was kind of the game,” Brown said. “We’ve got to be ready to go. Usually that group is really good to start the fourth and put pressure on the [other] team. Tonight, that wasn’t the case.”

The Celtics still had chances, but during a stretch midway through the fourth, Tatum missed a pair of 3-pointers and then had the ball knocked away, one slice of his forgettable night.