Cooper Flagg made his long-awaited NBA debut look effortless, sparking the Dallas Mavericks past the defending champion Oklahoma City Thunder in their preseason opener.

The first time Cooper Flagg touched the ball Monday night, the crowd leaned forward. By halftime, the top pick in the NBA draft had already given Dallas everything it hoped for.

The 18-year-old rookie finished with 10 points, six rebounds, three assists and a block in just 14 minutes as the Mavericks beat the defending champion Oklahoma City Thunder 106-89 in their preseason opener at Dickies Arena.

Mavericks coach Jason Kidd said the performance looked familiar.

“He was great,” Kidd said. “Cooper did an incredible job for us. You saw the defensive side, the playmaking and the scoring ability. He’s been doing this since training camp in Vancouver. He was really, really good tonight.”

Flagg’s first statement came on defense. Two minutes into the second quarter, Thunder guard Isaiah Joe slipped past his defender for what looked like an easy layup — until Flagg came flying across the lane to swat it away.

“We’ve been working our rotations defensively,” Flagg said. “Being the low man and rotating over, having my guys’ back — that’s what we’ve emphasized.”

Moments later, he found Dereck Lively II for a dunk, then started a personal scoring run that electrified the building. Over a span of less than three minutes, he drove for a layup, buried a three, drew a foul for two free throws and hit another long-range shot that pushed Dallas ahead 64-34.

“That’s the thing we worked on this summer,” Flagg said. “Just being comfortable expanding the floor, using the space this bigger court gives you and coming off pick-and-rolls ready to knock down open shots.”

Max Christie said the burst was no accident.

“I think he eased into the game really well,” Christie said. “His passing is really good, and the Thunder tried to pressure him a little bit, but he looked like he belonged. He filled up the stat sheet — scoring, rebounding, passing — and that early block set the tone.”

Kidd said Dallas plans to use that all-around skill set to its advantage.

“One of our strengths will be letting him handle the ball and make reads,” Kidd said. “He found PJ for an and-one and played off the dribble for threes. For an 18-year-old, that’s special. He’s only going to get better.”

Flagg’s shooting touch added another layer to his debut. He went 3-for-6 from the field and 2-for-3 from beyond the arc, a smooth integration of the perimeter work he emphasized during offseason training.

“I had a lot of fun,” Flagg said. “This is a great team — we’ve got a lot of really good guys, a lot of great players. We just played together really well, and that’s a fun brand of basketball when the ball’s moving around and everybody has each other’s back.”

Kidd praised the rookie’s approach as much as his production.

“He works extremely hard,” Kidd said. “He competes to win. He’s diving on the floor, making extra passes, doing everything to help his team win. Any drill, any scrimmage — the only thing he’s thinking about is winning.”

Christie said that competitiveness has already resonated inside the locker room.

“He’s picking up concepts really early, which is always good for a young guy,” Christie said. “This is probably the most uncomfortable he’ll be all season. It’s only going to get better.”

Flagg said the night was an important step in adjusting to the speed, spacing, and physical demands of the NBA game.

“It’s definitely different,” he said. “At Duke, by this time we’d had months of practices. Here, we’ve only had about two weeks. It’s just about coming together at the right time and figuring it out as we go.”

The Mavericks will host Charlotte on Saturday at American Airlines Center for their second preseason game, where Flagg will look to build on his sharp debut.

“Early in the game, throughout the game, whenever I was in there, I was just taking whatever the defense gives me,” he said. “Just keeping it simple — making the right play, whether it’s a pass, shot or whatever it is.”