Cooper Flagg’s first experience playing rival North Carolina was a cakewalk, and he was a big reason why.

The Duke freshman scored 21 points and added eight rebounds and seven assists as the No. 2 Blue Devils led by 22 points at halftime and rolled to an 87-70 ACC basketball win over the rival Tar Heels on Saturday night at Cameron Indoor Stadium.

The Blue Devils (19-2, 11-0 ACC) won their 15th game in a row, extending the nation’s longest active winning streak. It’s Duke’s longest winning streak since the 2012-13 team won its first 15 games.

A preseason all-American, Flagg made his presence felt immediately in helping Duke take control over the struggling Tar Heels (13-10, 6-5 ACC).

Flagg had a hand in Duke’s first 18 points, either scoring himself or picking up an assist. He had six points and four assists in the game’s first six minutes as the Blue Devils built a 23-6 lead.

Duke had scoring runs of 16-0 and 11-0 in the first half and had a 47-25 lead at intermission.

Duke led by as many as 32 points in the second half.

The Blue Devils shot 52.8%, making 10 of 20 3-pointers. Kon Knueppel’s 22 points led the Blue Devils while Tyrese Proctor scored 17 and Sion James 13 to give Duke four starters in double figures.

After shooting 29.6% in the first half, the Tar Heels heated up after halftime and finished with 47.3% shooting for the game. R.J. Davis and Drake Powell each scored 12 points for the Tar Heels while Seth Trimble added 10 points.

Here are three takeaways from the rivalry game:

Oh, how the Duke offense regained its groove

Duke had strung together seven consecutive games shooting 50% or better before failing to hit even 40% while beating Wake Forest and N.C. State on Jan. 25 and 27.

But the Blue Devils were blistering against the Tar Heels, hitting 11 of their first 18 shots. That included making four of the first seven 3-pointers.

The Blue Devils had gone all season without having more turnovers than assists in a game until committing 16 turnovers, while gathering 14 assists, in a 63-56 win at Wake Forest. Duke followed that up by committing 10 turnovers, with 10 assists, in its 74-64 win over N.C. State last Monday.

Against UNC, the Blue Devils returned to their season norm by collecting 20 assists, while turning the ball over only eight times.

Slow start returns for UNC

The Tar Heels, whose non-conference slate was defined by sluggish starts, found themselves facing a 27-point deficit with five minutes remaining in the first half.

Saturday marked the eighth time this season North Carolina fell behind by 10 or more points in the first half. In previous such instances, North Carolina rallied to beat Dayton and UCLA, but eventually lost to Kansas, Michigan State, Florida, Auburn and Alabama.

But this performance against Duke still stands out as more of an outlier than a trend. The Tar Heels’ 27-point hole marked the worst deficit North Carolina has faced all season (until UNC broke that record later in the evening, falling behind by 32).

As for the reasons, well, there are many.

The Tar Heels turned the ball over nine times in the opening half. North Carolina only recorded four fastbreak points, and when contained in the half court, struggled to get anything going.

Due to Duke’s elite rim protection, UNC converted on just eight of 17 layup attempts.

While North Carolina found its spurts in the second half, the team’s abysmal first-half performance made it clear the Tar Heels were outmatched by the Blue Devils on all fronts.

Maliq Brown returns

After missing Duke’s last four games and all but a minute of a fifth, 6-9 forward Maliq Brown returned to play for the Blue Devils on Saturday.

Suffering from a sprained knee, Brown had not played since Jan. 11, when he was on the court for less than a minute before suffering the injury. Duke won 86-78 over Notre Dame that day.

He sat out Duke wins over Miami, Boston College, Wake Forest and N.C. State. He returned to practice this week and was cleared to return earlier Saturday.

Brown made his first appearance with 14:51 to play in the first half and was the first reserve off Duke’s bench. That’s routinely been the case this season as Brown replaces Duke 7-2 freshman center Khaman Maluach.

It took only 11 seconds for Brown to make an impact as he knocked the ball away from UNC guard Elliott Caudau for a steal that led to Flagg’s fastbreak basket at the other end.