Flagg, 18, a consensus pick as the top US college player as a freshman at Duke University last season, is the second-youngest player taken first overall.
Superstar LeBron James was eight days younger when he was taken first overall in 2003 by the Cleveland Cavaliers.
“I’m feeling amazing. It’s a dream come true to be honest,” Flagg said after his name was called at the Brooklyn Nets’ Barclays Center arena, where his family was by his side. “I wouldn’t want to share it with anybody else.”
The Mavericks beat the odds to land the top pick in the draft lottery and as expected grabbed Flagg, who averaged 19.2 points, 7.5 rebounds, 4.2 assists, 1.4 steals and 1.4 blocked shots per game for the Blue Devils, who lost to Houston in the semi-finals of the NCAA collegiate tournament.
The 6-foot-9 (2.06m) player from Maine is a two-way playmaker with tremendous athleticism and a relentless presence on both ends of the floor.
Flagg could be just the player Dallas fans need to put aside the outrage triggered by the trade of star guard Luka Doncic to the Los Angeles Lakers for Anthony Davis in February.
That move broke up a squad that had reached the NBA Finals in 2024, but the Mavericks were hit with a stream of injuries in the 2024-25 campaign, which ended with elimination in the play-in tournament.
Flagg is now the third number one pick on the Mavs’ roster alongside Davis and Kyrie Irving, who is recovering from knee surgery.
The San Antonio Spurs took Rutgers University guard Dylan Harper with the second overall selection – the third straight year the Spurs have had a top-four pick.
In 2023, the Spurs made French star Victor Wembanyama the No. 1 overall selection and last year they took Stephon Castle with the fourth overall pick – both going on to earn Rookie of the Year honours.
Harper, the son of five-time NBA champion Ron Harper, averaged 19.4 points per game on 48.4 percent shooting.
In San Antonio he joins a Spurs team embarking on a new era after the official retirement from coaching of the legendary Gregg Popovich, who was sidelined much of last season after suffering a stroke.
Wembanyama is coming back from deep vein thrombosis in his right shoulder which limited him to 46 games last season, and the Spurs have missed the post-season in each of the last six campaigns. (AFP)
