BOSTON – It’s only 12 games in, but the Celtics are starting to reveal their vulnerabilities and it cost them a victorious start to their Emirates NBA Cup run as TD Garden’s clover-green parquet was anything but lucky.

Atlanta’s struggling Hawks visited Boston without the help of three-time All-Star Trae Young, De’Andre Hunter, Bogdan Bogdanovic and three others — two of their three scoring leaders — but none of that mattered. Atlanta’s Quin Synder’s undermanned roster humbly made the Celtics aware of how low Boston’s early shortcomings could drag the defending champs.

The Hawks defeated the Celtics, surprisingly, 117-116, through an unparalleled will to go one step further, despite four quarters of basketball – Boston and Atlanta combined to commit 35 turnovers. At the final buzzer of the fourth quarter, the Celtics could only hang their heads in regret and pain.

“They played harder and more physical than we did, and they got 20 offensive rebounds and forced 20 turnovers on us,” Celtics head coach Joe Mazzulla said. “You let a team overshoot you in the shot margin like this and you’re not going to win.”

Mazzulla added: “We got matched against them a few times, but they got rebounds and layups against everyone – big, small, medium. So they just beat us on both ends of the floor.”

Boston took a modest 31–29 lead in the second quarter, setting the tone for the overarching theme of the tournament-opening game; physicality, discipline and depth were the three decisive factors. The Celtics collected just six offensive rebounds to Atlanta’s 20, which accounted for 18 second-chance points from the Hawks. Boston’s 20 turnovers made the final score within inches of impressive for the Celtics, but spoke volumes about a problem that needed alleviation. Meanwhile, the reserve unit gave Mazzulla absolutely nothing from start to finish.

Payton Pritchard, an early candidate for Sixth Man of the Year, and Sam Hauser, Boston’s default marksman, combined for just nine points.

“They were just more aggressive and found a way to get every 50-50 ball, it seemed, and just wanted it a little bit more,” Derrick White said. “… It’s not really for us to come out and question our readiness, especially with the group we have.”

Jaylen Brown and Jayson Tatum were jointly responsible for eleven turnover figures. Boston’s star duo poured in 57 points, but also shot just 5-of-15 from 3-point range, while Brown missed four free throw attempts – including three in the fourth quarter. Even with the opportunity to make it right a lot of Shortcomings on the final possession left Boston short to recap a night of frustration and confusion.

Granted, it’s still early, but teams in the Eastern Conference — the Philadelphia 76ers (2-8), Milwaukee Bucks (3-8) and New York Knicks (5-5) — have experienced firsthand just how damaging a cold winter start can be. are for a team. Boston rarely experienced that last season, keeping every (rare) losing skit to no more than two games.

“Defense, setting the tone, physicality, too many layups,” Brown explained. “I think we guarded the three-point line well. Just physicality – shifting, rebounding. Those kinds of things we have to be good at from night to night. Tonight we weren’t. … Mentally, we were just too careless tonight. We expected victory. Too careless, and it showed.”

Boston fell to 9-3 on the season and still trailed only the undefeated (12-0) Cleveland Cavaliers for the lead in the East. There’s still plenty of time, especially without Kristaps Porzingis, meaning the Celtics have plenty of wiggle room to live and learn from their mistakes as the season progresses.

“This is part of the journey, but we have to clear out some stuff,” Brown said. “We are not a perfect team. It’s a new season. It’s a new journey and we look forward to embracing those moments.”