CHAPEL HILL, N.C. -- Two overwhelming runs showed just how good North Carolina (No. 4 ESPN/USA Today, No. 3 AP) can be. In between, the Tar Heels allowed struggling Boston College to make things tense -- and showed there's still plenty of room for improvement.

"At times, we were very good," forward Tyler Zeller said. "Other times, we weren't."

Harrison Barnes scored nine of his 25 points during a late run that helped North Carolina turn a close game into an 83-60 rout Saturday in its Atlantic Coast Conference opener.

Zeller added 20 points for the Tar Heels (14-2, 1-0). The preseason league favorites shot 47 percent, took control with a big first-half flurry and used an even bigger spurt late to claim their eighth straight win and 27th in a row at the Smith Center.

North Carolina led by 21 points early in the second half before BC -- and its starting lineup of five freshmen -- tried to claw back.

"Sometimes, when we get a good lead, we let up defensively and we just want to run out and score," forward John Henson said. "I think we've got to just play D a little harder -- especially when we're up by a lot, just push it a little farther."

The Eagles made things interesting when Patrick Heckmann's 3-pointer trimmed the Tar Heels' lead to 59-50 with 9:18 left.

"I told them it was very reasonable that I was upset and they had to play better," North Carolina coach Roy Williams said. "(But) we were good at times."

Their best came two possessions later when Barnes answered with a slashing drive that started the 22-8 run that pushed the lead back into the 20s. Barnes also capped the run with a free throw that made it 81-58 with 2:13 left before he exited to an ovation.

Zeller added eight points during that late surge.

"I thought we let our guard down and ... we just kind of forgot who we were playing and lost sense of simple things," BC coach Steve Donahue said.

Matt Humphrey scored 14 points and Ryan Anderson added 13 for BC (5-10, 0-1), which had 20 turnovers in losing its third straight.

Henson added 14 points, Kendall Marshall had 11 assists and Barnes reached 20 points for the third time in four games for North Carolina, which surely remembered how uneasy the Eagles made things in their last visit to the Smith Center -- especially as they threatened for a while to do it again.

Boston College slowed it down last February and came within a rimmed-out 3-pointer at the buzzer of a memorable upset. Instead, North Carolina escaped with a 48-46 victory in its lowest-scoring performance at the 26-year-old arena.

"We just went at them" this time, Humphrey said. "They probably expected us to make it a grinding game and slow it down, but in reality, that's the way we play as well. We just should have kept a little bit more poise and saved some of those turnovers."

The Tar Heels had nearly that many points at halftime of this one, racing to a 40-27 lead at the break.

Barnes scored 12 in the first 20 minutes, and after North Carolina let BC hang around for a little while, it grabbed control by cranking up the defense -- and letting the young Eagles make plenty of mistakes.

After Boston College hit six of its first 11 shots, the Tar Heels forced BC into nine consecutive empty possessions as part of the 18-5 run that put them in command -- for a while, anyway.

BC turned it over 11 times in the half, and the defining play came on a sequence that could have been miscue No. 12. Heckmann let a long heave fly with the shot clock about to expire, Henson grabbed it out of the air and passed ahead to Marshall -- who found Barnes for an authoritative dunk that pushed the lead to double figures.

"When it looked like Carolina was going to shove us out the door, I thought these guys showed a lot of character and toughness," Donahue said.