GREENSBORO — With less than six minutes left Sunday and top-seeded North Carolina trailing by 10, Tar Heels point guard Kendall Marshall found a rarely-open Harrison Barnes for a transition 3-point opportunity.

When it missed, so did top-seed UNC’s opportunity for a third straight double-digit comeback in this ACC tournament, and its chance at a 10th straight victory. Duke blew out the Tar Heels 75-58 at Greensboro Coliseum.

“You’re not going to make every shot,’’ said Marshall, who finished with more turnovers (five) than assists (four). “But at that point, it was kind of a heartbreak, because you think, if you hit that, the momentum’s on our side, it’s a 7-point game, three possessions, we’d face the same position we’d be in the last three days.”

One of the biggest problems for the Tar Heels – who shot 33.9 percent, committed 16 turnovers and watched the Blue Devils make half of their baskets – was their failure to get Barnes the ball in the correct positions, and Barnes’ failure to convert most of the times he got it. Coming off an 18-point outing against Miami in the first round, then a tournament-freshman-record 40 points against Clemson on Saturday, he was a key reason why UNC was able to come back from 19- and 14-point deficits, respectively.

But as the focus of No. 2 seed Duke’s defense, covered predominantly by Blue Devils senior Kyle Singler, he made only 6 of his 15 shots (and 1 of four 3-point attempts), finishing with 16 points.

“It was no surprise after yesterday’s game; they had a team-oriented defense around me, a lot of switching on screens … the bigs held my penetration, and I needed to do a better job of getting my teammates involved,’’ Barnes said.

Singler said his goal was to limit Barnes’ touches and force him to take tough shots, but "we had a great scouting report and we followed the game plan pretty well. It wasn't all on me. It was a team defensive assignment.”

Even with his struggles, Barnes was a big reason for UNC’s late push.

His only 3-pointer of the day, with 6:39 left, cut the Tar Heels’ deficit to 63-52. Then his jumper 38 seconds later cut it to 54-63.

But after Marshall followed Duke guard Seth Curry’s 3-pointer with two free throws to make it 66-56, Barnes missed that pivotal 3-pointer from the wing. “And I turned to our bench and said, ‘Boy, that would have been fun if we had gotten it down to seven,’” UNC coach Roy Williams said.

Instead, Blue Devils forward Ryan Kelly followed with a 3-pointer at the other end, beginning a game-ending 9-2 run for Duke (during which Barnes made UNC’s only two points, on free throws).

“They did a great job,’’ Williams said. “Kyle Singler, another senior, was guarding [Barnes] and made it tough for him. Some of his shots didn’t go in as easily today as they did yesterday, but sometimes he lost a little patience, too.”

Robbi.pickeral@newsobserver.com or 919-829-8944