DALLAS -- As Cooper Flagg settled into his seat in the interview room, he instantly felt regret.
"Oh, I forgot my peanut butter and jelly," Flagg said, referring to the sandwiches he's been caught eating during recent games as he prioritizes putting weight on his 19-year-old frame. "I was supposed to bring the peanut butter and jelly. Dang it!"
Flagg did pretty much everything else right on Monday night, when he stuffed the box score with 43 points, 10 rebounds, six assists, three steals and a block in the Dallas Mavericks' 125-122 win over the Indiana Pacers.
Flagg, the reigning Rookie of the Year, joined Kevin Durant as the only teenagers in NBA history to produce a 40-point, 10-rebound line. It was the fifth 40-point performance of Flagg's career; the rest of the teens to play in the league have combined for a total of 10.
"It's unbelievable he's a 19-year-old doing this," Mavericks coach Dusty May said.
The elder statesman on the Mavericks' roster was pretty impressive, too. Kyrie Irving, playing in both games of a back-to-back for the first time since recovering from a torn ACL that sidelined him all of last season, scored 35 points on 11-of-18 shooting in 38 minutes.
Flagg and Irving combined for 26 points in the fourth quarter as the Mavericks closed out the Pacers to improve to 7-4.
"Tonight me and Kai had it going," said Flagg, who was 16-of-25 from the floor and 3-of-6 from 3-point range. "There's hopefully going to be a lot of nights like that."
Irving, 34, an eight-time All-Star, long ago established himself as one of the NBA's elite scorers. Flagg has already joined that company, averaging 25.9 points on 50% shooting from the floor this season.
Flagg is also averaging 6.9 rebounds, 6.9 assists and 2.0 steals per game. The only other player in the league averaging as many points, rebounds, assists and steals per game: Luka Doncic, the former Mavericks star who is on a historic tear for the Los Angeles Lakers.
"We keep calling him a teenager, but he plays ways beyond his years," Irving said. "Gotta give him his flowers. The way he's always in attack mode, the way he sees the game and he gets others involved -- very selfless it helps out our team a lot, including myself. Just seeing him being able to make plays for others, but also when he's calling his own number, he's getting in that paint and trying to get the most efficient shot possible."
The midrange jumper has become an extraordinarily efficient shot for Flagg. He put the finishing touches on his 43-point performance with a pair of pull-up 18-footers in the final minute. According to NBA.com tracking, Flagg has shot 29-of-49 (59.2%) on attempts between 10 and 19 feet this season.
"I think just being able to get to my spots at a higher level and being more comfortable with that has allowed me to take a little bit of load off my body," Flagg said. "Just kind of stop it short, raising up over people. It's taxing to get downhill all the way to the rim and try and finish over 7-footers all night every night. I think just adding that in there, it definitely allows me to pace myself a little bit."
Flagg is flourishing as a clutch scorer in his second season. He ranks fourth in the league in clutch scoring with 27 points on 11-of-13.
"I'm not even going to lie: I didn't think he was going to be this good," Mavericks forward Naji Marshall told ESPN. "I knew he was good. I didn't think he was going to be this good. Every day, bro, he just breaks the standard for what I thought he was going to be."