The Celtics-Suns game on Thursday seemed a lot like a track meet in the first half. Both teams scored at least 60 points by applying constant pressure to the ball.

Jayson Tatum scored 14 points in the first frame and 23 points at the interval on the 9/11 shooting, keeping pace from the opening tip. As the second quarter came to an end, he made two baskets over Kevin Durant and finished with a perfect 4/6 from beyond the arc. 

Even though Boston gave up 13 offensive rebounds and 15 second-chance points while struggling to stop Phoenix from shooting, the hosts can attribute their 65-60 halftime advantage to the way they closed the first quarter.

Joe Mazzulla lectures about how crucial it is to end a quarter on a positive note because it sets the tone for the next one. Thursday’s 10-2 final to the first quarter saw the Celtics dramatically improve their defensive performance, finding newfound vigor that allowed them to stall drives, contest shots, and force turnovers—all of which ignited their offense.

Jaylen Brown took over from there, feeding off the fervent supporters at TD Garden. He repeatedly bullied his way past the chests of opponents, including Bradley Beal’s, to score 15 points in the second quarter and 20 by the half.

Following the interval, Boston performed a far better job of combining strong first-shot defense with a restriction on the visitors to one attempt per possession. The visitors were limited to just two offensive rebounds by the C’s, who also outscored them 6-2 on second-chance points.

In addition, they received eight points from Sam Hauser, witnessed the continued success of Xavier Tillman and Al Horford’s combination without sacrificing spacing, and went into the last quarter having converted 12 turnovers by the Suns into a 16–6 lead in points off turnovers.

They were able to keep up their fast-paced play, frequently make good, rhythmic shots, and extend their advantage to 102-85 going into the final 12 minutes.

And Phoenix was unable to stop Brown, who finished with a game-high 37 points, and the hosts continued to shoot well from three-point range, making 25 of 48 (52.1 percent) of their attempts before running out of bench players. The Celtics also held Phoenix to 1/4 shooting from long range before the extended rotation put the finishing touches on a 127-112 victory for Boston.