LAS VEGAS — No. 1 pick Cooper Flagg managed to make the most important play in what he described as “one of the worst games in my life.”

Flagg swooped in from the weak side to swat away Los Angeles Lakers guard DJ Steward’s driving layup attempt with 1:10 remaining in Thursday night’s NBA 2K26 Summer League opener. Flagg then pushed the ball down the floor in transition, drew three defenders as he approached the paint and found teammate Ryan Nembhard wide open for a 3-pointer that gave the Dallas Mavericks the lead for good in an 87-85 win.

Flagg’s shooting struggles (5-of-21 from the floor, 0-of-5 from 3-point range) stand out in the box score, but his coaches consider the defensive stop and assist to be the defining moment of the game, a sequence that encapsulated Flagg’s competitive character and all-around impact.

“That’s what he does,” said Mavs assistant Josh Broghamer, the team’s summer league head coach. “He makes winning plays, whether it’s offense or defense. I think that’s as advertised. So whether it’s the right pass or it’s a defensive possession or scoring the ball, that’s what he does.”

Dallas coach Jason Kidd directed that Flagg frequently be used as a point guard during summer league, challenging the 6-foot-8, 220-pound forward to expand his game as a primary facilitator. The Lakers appeared determined to make Flagg as uncomfortable in his new role as possible, trapping him at half court the first time he touched the ball and defending him physically throughout the night.

“I thought that was out of respect,” Kidd told ESPN’s Malika Andrews at halftime, referring to the double-team on the opening possession. “When you have someone like Cooper, who can handle, who can shoot, who can pass, you want the ball in his hands. He’s a great decision-maker. He did that at Duke. He did that at high school. He’s going to have some mistakes. We all did. We all threw it in the stands once in a while. But I think just his poise as an 18-year-old is incredible.”

Flagg, who finished with 10 points, 6 rebounds, 4 assists, 3 steals and the block, displayed his ability to handle the ball and pass during his summer league debut. He couldn’t find a rhythm as a shooter, making only 2 of his 17 attempts outside of the restricted area, and admitted that it felt odd to launch so many jumpers.

“The coaches have a lot of confidence in me,” Flagg said. “They were telling me they want me to experiment, try some new things. I was trying to be aggressive. That’s new for me, too.

“I would say that might be one of the worst games of my life. We got the win, so that’s what really matters to me.”

Flagg especially struggled in half-court sets, as all but one of his buckets came in transition. The exception was a tough midrange turnaround over Bronny James, which occurred immediately after James was called for a foul after poking the ball away from Flagg on a post-up, a call booed by the Thomas and Mack Center crowd that buzzed every time the No. 1 pick engaged in an individual matchup with all-time leading scorer LeBron James’ son.

“He’s got like a half a foot on me, so I’m just trying to stand my ground,” Bronny James said. “I got to stand my ground down there and make sure I’m not getting bullied anywhere on the court. … He’s great. I mean, I watched him all in college and he’s an amazing player. I have the utmost respect for him. He’s going to be something special.”

Flagg wowed the crowd on multiple occasions with spectacular plays in transition, displaying his blend of athleticism and ballhandling ability.

His first basket was a tomahawk dunk in traffic midway through the first quarter, finishing a fast break that he started with a steal. He pushed the ball again the next possession, pulling up for a baseline fadeaway over 2024 first-round pick Dalton Knecht. Flagg also had an and-1 layup after receiving a lookahead pass and a pretty finish over former first-round pick Darius Bazley after going coast-to-coast.

Flagg, who averaged 19.2 points on 48.1% shooting during his lone season at Duke, acknowledged some frustration with his inability to score out of half-court sets Thursday but added that he wasn’t worried about it.

“Shots weren’t falling, but that’s going to happen,” Flagg said. “It’s going to be nights like that. It is somewhat new to me. I haven’t probably taken that many shots before, so that’s somewhat new. I’m going to try and figure it out. But new experience, so I’m excited to keep playing and move forward.”