As their winning streak reached six games, the Celtics’ flaws were masked by victories. Wins in Toronto and Memphis over the weekend were marred by poor efforts, but the C’s kept finding ways to win anyway. Even after winning Sunday night over the Grizzlies, coach Joe Mazzulla said his team shouldn’t have won.

A night later, the Celtics got the outcome they deserved.

Through the first 13 games of this season, the Celtics had seemed to solve the crunch-time woes that killed them throughout last season. But they took a big step back on Monday night. Even without Derrick White, the Celtics had more than enough to close out the lowly Hornets but their bad habits resurfaced in a brutal 121-118 overtime loss.

Jayson Tatum scored 45 points and Payton Pritchard added 21 in a big effort off the bench in the absence of White, but the Celtics’ recent run of uninspired play finally came back to haunt them. The Celtics led by as many as 18 in the first half but let the Hornets stick around. Then they blew a nine-point lead over the final two minutes of regulation that was a culmination of the lazy play that has plagued them over the last three games.

“We had 29 points in transition given up, (they had) 20 second-chance points, 17 offensive rebounds, that’s not a recipe for success no matter who you’re playing, especially these guys,” C’s coach Joe Mazzulla told reporters in Charlotte. “They don’t stop playing.”

LaMelo Ball scored 36 points with nine rebounds and eight assists to lead the undermanned and seemingly overmatched Hornets, who made enough plays to linger throughout the night before striking the Celtics in crunch time.

The Celtics led 100-89 and seemed to be in firm control after Jrue Holiday’s 3-pointer with 2:20 remaining. But then they let their foot off the gas. Mark Williams ignited the Hornets’ surge with a second-chance tip-in layup with 1:59 left before the Celtics began misfiring offensively. Ball hit a 3-pointer to make it 108-104 and then after two more Celtics misses, Williams’ second-chance layup cut Boston’s lead to two with 34 seconds remaining.

On the next possession, Holiday was fouled at the rim by Ball with 11 seconds left and went to the free throw line with a chance to make it a two-possession game. But Holiday, who committed seven turnovers in the loss, missed both free throws. They were Boston’s first two free throw misses in crunch time this season.

On the next possession, Ball’s driving layup tied the game and ultimately forced overtime after Sam Hauser’s long 3-point attempt missed.

The Celtics had four leads in overtime, including Tatum’s 3-pointer with 58 seconds left. But on the next possession, the C’s lost Gordon Hayward cutting for a game-tying dunk. Jaylen Brown then missed a 3-pointer, and on the next Hornets possession, Miles Bridges drilled a desperation 3-pointer at the buzzer to give them a 119-116 lead.

The C’s called timeout and got a gift as Tatum was fouled by Hayward shooting a 3-pointer. He went to the line with a chance to tie the game, but after making the first two, he missed the third. Bridges pulled down the rebound and was fouled with 1.7 seconds left.

But there was some controversy. It appeared Bridges was fouled with about 3.2 seconds remaining, but the clock kept ticking. The clock was not checked by the officiating crew. The Hornets inbounded the ball again because the C’s had a foul to give and Hayward was fouled with 0.8 seconds left, which gave Boston little time to make a play after his free throws pushed Charlotte’s lead to 121-118. Bridges intercepted the final inbounds pass to clinch the Hornets’ victory, and gave the C’s more lessons to learn as they headed home from a road trip that gave them plenty.

“You just have to take something from each game, and so this was our first overtime game where it was the first time we blew a lead and we have to go back and understand why we did it, and it comes from taking plays off and not finishing possessions,” Mazzulla said.

Other takeaways and notes:

– The C’s, on the second night of a back-to-back, were seemingly on fumes in the fourth quarter. In addition to the absences of White and Al Horford, Brown was on the bench in foul trouble. The Celtics were barely holding on as Mazzulla went to a unique bench lineup that included Pritchard, Hauser, Svi Mykhailiuk, Oshae Brissett and Luke Kornet to start the final period. But the unit had an impressive stretch in a critical moment.

After they gave up back-to-back buckets to start the quarter, Mazzulla called timeout but the unit responded with a 10-4 surge led by Pritchard, who made several big plays including a highlight-reel driving layup. The bench lineup handed a 97-89 lead back to the starters midway through the fourth before they failed to hang on. But it was an important moment as Mazzulla continues to look to trust his bench in those situations.

– Tatum continued to dominate the Hornets, especially in Charlotte, where he has several fans from his playing days at nearby Duke. After an awful performance Sunday, when he committed eight turnovers and only took one 3-pointer, Tatum bounced back in a big way as he scored 31 points in the first half, matching his career-high for first-half points. Tatum is now averaging 41.5 points in his last six games against the Hornets.

– White missed Monday’s game due to personal reasons, while Horford missed the game due to rest as he continues to sit one game of back-to-backs. It’s unclear if White will return for Wednesday’s game against the Bucks. Hauser took White’s place in the starting lineup, but the hot-shooting forward cooled off as he went just 1-for-9 from long range in 37 minutes.