Updated

When North Carolina plays well, the 11th-ranked Tar Heels are a tough group that can win close games. When they don't, the results have been ugly.

With Sunday's 84-63 loss to No. 5 Duke, all three of the Tar Heels' defeats have come by lopsided margins. It's a curious stat for a team that has won all six games decided by four or fewer points this season and entered February right behind the Blue Devils at the top of the Atlantic Coast Conference standings.

North Carolina was routed by 45 points at Tennessee in December and by 26 points at Maryland last month. This time, they fell behind by 33 points on the way to a 21-point loss to the Blue Devils.

Compare that to last month, when the Tar Heels beat then-No. 8 Maryland, Virginia Tech and North Carolina State in succession by a combined 10 points. Last weekend, the Tar Heels won at Miami on Danielle Butts' jumper at the buzzer for their latest close victory.

It's left coach Sylvia Hatchell searching for a way to improve the mental toughness of players who have shown exactly that in several tight games. Hatchell was going for her 900th victory to become only the third coach in women's basketball to reach that milestone, along with Pat Summitt and Jody Conradt.

"The three games we've lost, we've had a bad run somewhere ... that's really, really hurt us," Hatchell said. "Some of that I think is just developing mental toughness. And on my part, I guess we can slow them down a little bit and maybe try to do some other things out there. But usually when this group is going out there, you don't want to get in their way — you want to let them go and play."

For Duke, Chloe Wells scored a career-high 18 points, while Tricia Liston added 15 off the bench.

The Blue Devils (20-1, 10-0 ACC) jumped all over the Tar Heels to take the drama out of this one early. Duke blew the game open with a 29-3 run over 10 minutes and led by 31 at halftime in its fifth straight win in the rivalry.

The Blue Devils shot 56 percent, hit 7 of 9 3-point attempts and kept adding to the lead by cashing in on turnovers or the offensive glass during the dominant first half. The Tar Heels (20-3, 8-2), meanwhile, shot just 22 percent and had twice as many turnovers (14) as field goals (7) in the half.

North Carolina finally showed some fight after halftime but still never seriously threatened a comeback. The Tar Heels pulled to within 60-42 with 12½ minutes left on Brittany Rountree's layup off a turnover, but Liston answered with a 3-pointer and a spinning basket in the lane to shut down what amounted to UNC's best push.

Tierra Ruffin-Pratt scored 18 points to lead the Tar Heels, but she had 11 of the team's 24 turnovers. North Carolina shot 33 percent for the game in its first home loss.

Hatchell's next chance at her 900th win will come Thursday at Boston College.

The Blue Devils — who beat UNC by 40 points at home last season — were 11 for 18 from behind the arc, with Wells going 6 for 7. Duke also had 24 points off turnovers and 25 second-chance points.