GREENSBORO, N.C. -- Jim O'Brien believed Ohio State would play good defense against No. 4 Duke after holding third-ranked Alabama to 54 points last week.

But the Blue Devils can make good defensive teams look silly at times.

J.J. Redick scored all 20 of his points in the second half and Daniel Ewing added 18 as undefeated Duke used a 21-3 run to start the second half and rolled over the Buckeyes 91-76 in the ACC-Big Ten Challenge on Tuesday night.

''Those guys are a high-octane offense,'' O'Brien said. ''They can go in blitzes. They are very good at stretching the defense and can go by you on the dribble. They sure put pressure on you.''

Ewing did most of his work keeping Duke (4-0) close in the first half with 13 points before Redick, in his first collegiate start, went 5-for-8 from the field in the final 20 minutes while making all six of his free throws.

Redick had two 3-pointers and Chris Duhon one during an 11-0 spurt to start the period as Duke went up 52-33, forcing O'Brien to call a timeout.

The Buckeyes needed two more in the next two minutes in an attempt to slow down Duke, but the stoppages just prolonged the inevitable.

Redick added a three-point play and three free throws, Duhon scored on a driving layup and Shelden Williams had a fastbreak dunk to push the score to 62-36 lead.

The only thing that stopped Redick's hot hand was a bloody nose midway through the second half.

''Our effort was great,'' said Redick, who leads Duke with a 17.3 scoring average. ''That first 10 minutes of the second half was the best we've played season. We're really excited about what we did.''

Brent Darby, with a 8.7 career scoring average, led the Buckeyes (1-2) with a career-high 35 points. His previous best was 26 against Northwestern last season.

''Darby had one of those fantastic performances,'' Duke coach Mike Krzyzewski said.

Darby had 10 straight points as Ohio State closed to 75-67 with 4:32 left after trailing by 27. But Redick hit a 3-pointer and Ewing made two free throws two minutes later as the Blue Devils went back up by 14 and sealed the game at the foul line.

''I think we were too happy to where we thought the game was over and a team like Ohio State doesn't quit, they have too much tradition and too much pride,'' said Duhon, who matched his career high with 13 assists.

But in the end, it was just too much Redick, who notched his second straight 20-point game. The 6-foot-4 freshman guard also had that many over the weekend against UCLA.

''He's just warming up, but it's going to get tougher for him because guys are recognizing how well he shoots the ball,'' Duhon said. ''They are going to be running out to him.

''We've got to set better screens and he's going to have to do a better job of reading the defense and giving head fakes. But he's a weapon we're going to keep using.''

Redick is up for the challenge.

''The game has kind of slowed down a little bit for me, which is nice,'' he said. ''It gives me time to think a little bit.''

For the fourth time in as many games, Duke placed four players in double figures and is beginning to mature.

''I am not surprised. I think our team is developing well,'' Krzyzewski said. ''We're really playing hard. We've got to stay the course and we'll keep getting better. I don't think our team is going to make drastic jumps. It's going to be a little bit at a time.''