Before Friday’s game against the Jazz, Celtics coach Joe Mazzulla was asked why his team is so elite defensively. His answer was mildly surprising considering his team entered the night ranked third in defensive rating.

“I don’t think we’re there yet, but I think we’re working on it,” Mazzulla said.

A few hours later, the Celtics took another step in that direction.

The Celtics were not sharp defensively on Tuesday night in Oklahoma City, leading to a rare loss for this group, but three nights later – with some fresh legs and back at comfortable TD Garden – they responded. They swallowed the inferior Jazz from the opening tip and never let up in a dominant 126-97 victory that was rarely in doubt.

Jayson Tatum scored 30 points, which included a season-high 13 free throws, Kristaps Porzingis had 19 and Jrue Holiday contributed 14 as the Celtics made quick and easy work of the surging Jazz – who were winners of nine of their previous 12 games – in this convincing romp. The blowout allowed Mazzulla to give his starters some critical extra rest ahead of Saturday’s back-to-back in Indiana, as they all sat out for the entirety of the fourth quarter. The Celtics improved to 17-0 at home this season.

On Friday, the Celtics set the tone in the opening minute. After they committed a turnover on the opening possession, Tatum raced back in transition to block Kris Dunn’s layup attempt. Moments later, Jaylen Brown produced a clean block of Jazz star Lauri Markkanen at the rim.

It seemed to spark the Celtics on both ends as they jumped out to a 10-0 lead. The Jazz missed their first nine shots of the game before a dunk from Markkanen. But after Porzingis drained a 3-pointer midway through the opening period to put the Celtics back up 10, the Jazz never cut their deficit back to single digits.

The Celtics suffocated them defensively. On one play, Oshae Brissett stripped Jordan Clarkson and dove on the floor for the loose ball, leading to a break in which Brown found Sam Hauser for an alley-oop dunk. The Celtics held the Jazz to just 15 first-quarter points, limiting them to 5-for-29 shooting.

It snowballed in the second quarter, which got ugly for the Jazz. The Celtics’ bench group of Tatum, Holiday, Hauser, Payton Pritchard and Luke Kornet dominated as they went on a 20-4 run that essentially put the game away. At one point in the quarter, the Celtics were tripling up the Jazz, 54-18. Midway through second, Tatum had more points by himself than the Jazz, who started the game an almost unbelievable 6-for-39 from the field. The Celtics led by as many as 36 points and by 31 at halftime.

The Celtics, after a terrible third quarter on Tuesday, did not relax and let the Jazz get back into it on Friday as they led by more than 30 for almost the entire period. Tatum – who had an encouraging shooting night by going 5-for-8 from 3-point range and 13-for-14 from the free-throw line – exited with 4:01 remaining in the third. His fellow starters soon followed, as did Gino Time.