The Celtics‘ hopes of stacking an NBA Cup title on top of last season’s championship got off to a rocky start Tuesday night, writes Brian Robb of MassLive. Jaylen Brown blamed a lack of focus as Boston squandered a 15-point second half lead while losing at home against Atlanta.

“I think mentally we were careless tonight,” he said. “We expected to win. Too careless and it showed. I think the No. 1 category it showed in is our turnovers. Uncharacteristic of us to have 20 turnovers in any circumstance. I think that just displayed that we weren’t in sync like we normally are, so we’ve got to be better at that, and I’ve got to be better at that.”

Following a 7-1 start, the Celtics have gone 2-2 in their last four games and are now three games behind Cleveland in the race for the top spot in the East. Their wins over the weekend against Brooklyn and Milwaukee came after slow starts in both games.

“It’s just a mentality,” Brown said. “This is a part of the journey. We’ve got some stuff to clean up. We’re not a perfect team. It’s a new season, a new journey, and we’re looking forward to embracing those moments. We’re going to watch it and we’re going to address what needs to be addressed.”

There’s more from Boston:

• Jayson Tatum is no longer on the injury report after being listed as questionable with soreness in his left ankle prior to Tuesday’s game, Robb adds in a separate story. Tatum turned his ankle during Sunday’s contest, but was able to keep playing.
• The Celtics continue to have matchup problems with big, physical teams, observes Gary Washburn of The Boston Globe, as the Hawks collected 20 offensive rebounds and scored 38 second-half points in the paint. Atlanta’s center tandem of Clint Capela and Onyeka Okongwu shot a combined 15-of-22 from the field. “They got rebounds and layups on everybody, bigs, smalls, mediums,” coach Joe Mazzulla said. “They just outplayed us at both ends of the floor.”
• Mazzulla told reporters that he would prefer to see the NBA Cup as a standalone event rather than having the games count in the regular season standings, per Adam Himmelsbach of The Boston Globe. He compared it with tournaments held in European soccer. “They don’t count toward your domestic league,” Mazzulla said. “It’s its own league entirely. That, to me, is my only negative toward it. I like it. I think having something like it in the middle of the season is good, especially in a long year. Just, that’s the difference between what you do here and what you do around the world. But it’s an opportunity for us to win something, an opportunity for us to go after something. So we’re going to go after it from that perspective.”