Jayson Tatum was well-rested Friday after sitting out the Celtics’ win over Milwaukee two nights earlier.

He certainly looked it against the slumping Hornets.

Tatum racked up 34 points on 9-of-16 shooting, eight rebounds and nine assists in just 29 minutes as Boston routed Charlotte 119-80 in its second game of NBA Cup group play.

The Celtics star was well on his way to his first triple-double of the season when head coach Joe Mazzulla shut him down late in the third quarter.

“I took last game off, so I was anxious and ready to get back on the court,” Tatum said in a postgame interview with NBC Sports Boston’s Abby Chin. “And, you know, Cup game, so we were trying to get this one.”

Boston maintained its 39-point margin of victory — an important NBA Cup tiebreaker — through the fourth quarter while Tatum and its other starters watched from the bench.

Derrick White contributed 18 points and five assists — all in the first half — and made four of his six 3-pointers. Tatum went 5-for-8 from deep and 11-for-11 from the foul line.

As a team, the Celtics shot 24-for-44 from 3-point range (54.5%), with 10 different players hitting at least one. They improved to 7-2 on the season and 2-0 in Cup play. The Hornets fell to 3-7 and 0-2.

With Tatum back after his rest-day DNP and Payton Pritchard (12-6-5 in 23 minutes) cleared to play after leaving Wednesday’s 109-102 win over the Bucks with an eye abrasion, Mazzulla had his full rotation available for the full time in a week. He tweaked his starting lineup, reinserting Jordan Walsh after bringing the fourth-year wing off the bench in the previous three games.

It was the fifth different starting unit Mazzulla has deployed in nine games this season.

The Hornets, who overhauled their roster this offseason by trading away LaMelo Ball and Miles Bridges, were missing a slew of key pieces from their new-look group.

Last season’s Rookie of the Year runner-up, Kon Knueppel, was inactive after aggravating a hamstring injury on Wednesday. Starting center Moussa Diabate (quad) and veteran guard Dennis Schroder (thigh) also sat. Leading scorer Brandon Miller suffered a groin injury before halftime and did not return.

Between injuries and roster turnover, these opening weeks have been a slog for Celtics assistant-turned-Hornets head coach Charles Lee, whose squad carried a five-game losing streak into Friday night. After posting the NBA’s best offensive rating from January on last season, Charlotte came in ranked dead last in that metric and 26th in net rating.

Those woes continued.

The Celtics raced out to an 18-4 lead and led 40-20 after the first quarter. They hit seven of their first 10 3-pointers; the Hornets started 2-of-14 from distance.

Tatum nearly outscored the Hornets by himself in the first. He poured in 18 points. including a personal 11-2 run late in the period. Among his six first-quarter makes were three 3-pointers and two and-ones. He also assisted on four other Boston triples, including two by White, who scored seven points in 15 seconds during the Celtics’ early deluge.

Add all of those up, and Tatum either scored or assisted on 30 of the Celtics’ 40 first-quarter points. It was the second-most productive quarter of his NBA career, trailing only a 32-pointer against Washington in the 2021 play-in tournament.

The second quarter featured more of the same from Tatum and White. By halftime, the former had scored 24 points and created another 18 through assists (42 total). The latter had generated 32 total points — 18 of his own, plus another 14 via assists.

The Hornets managed just 39 first-half points. The Celtics were doubling them up with three minutes remaining in the half and took a 70-39 lead into the locker room.

“At the end of the first quarter, Joe asked us, ‘Are we playing well, or are we just making shots?’” Tatum told Chin. “Sometimes that can get lost. You feel like you’re playing well just because you’re making shots. So I think in that second quarter, we really turned it up on the defensive end. It always helps when you make shots, too.”

Unlike in their NBA Cup opener, when the Celtics led Chicago by 29 points at halftime but won by just 14, and Wednesday against Milwaukee, when they coughed up a 22-point lead before rallying late, there was no second-half letdown here. Free throws by Tatum with 1:01 to play in the third quarter stretched the lead to 42 points.

Those were Tatum’s final contributions of the night. Deep reserves Mike Conley and Ron Harper Jr. entered in the fourth quarter and helped push the lead to 46 points.

The Celtics are the lone 2-0 team in NBA Cup East Group C, which also includes the Atlanta Hawks and Washington Wizards. Their point differential, which will break any ties that can’t be settled by head-to-head record, is plus-53.

“We’ve yet to make it to the (Cup) finals,” said Tatum, whose team’s deepest run was a trip to the 2023 In-Season Tournament quarterfinals. “It’s obviously not the ultimate goal, but it’s important. You want to compete, and it’s something to try to win, so you’ve got to go after it.”

Friday’s win opened a four-game road trip for the C’s. They’ll head to Milwaukee on Sunday for a Bucks rematch before traveling to Philadelphia for one of the most anticipated dates on their early-season schedule.

Boston’s first regular-season matchup with Jaylen Brown and the 76ers is set for Tuesday.