North Carolina (19-7, 9-4 ACC) has yet to allow an opponent to shoot 50 percent from the floor this season. With 15 minutes to play, however, Duke (21-6, 10-4 ACC) was hitting at a 55 percent clip (22-of-40) and leading 51-40.
The Blue Devils, known as always for their lights-out tendency from long range, had taken advantage of UNC's extension on the perimeter to penetrate and get to the rim. Duke was shooting 62.1 percent (18-of-29) from inside the arc up to that point.
After James Michael McAdoo rebounded a Leslie McDonald miss and slammed down the putback to pull UNC within 53-47 with 12:11 to play, Williams frantically motioned to his players as they retreated on defense.
UNC switched briefly into its 3-2 drop zone before turning to a new defensive wrinkle – a 1-3-1 trap zone, or "13" as the team calls it. It was the first time Williams has run the scheme all season.
The zone look, while gifting Duke a handful of looks from behind the arc, limited the Blue Devils' ability to penetrate. Williams rotated the 1-3-1 with his base man-to-man over the final 10 minutes, effectively keeping Mike Krzyzewski and his players guessing.
"It was changing pace and tempo," McAdoo told reporters following the game. "Most of the game they were able to break us down off the dribble. That (zone) helped us keep the ball out of the middle of the court…
"We were able to make them uncomfortable with the different defenses."
As a result, Duke missed its next 13 field goal attempts and completely lost its offensive effectiveness. The Blue Devils scored 13 points over the final 12:11 and shot just 21.7 percent (5-of-23) to close.
If there's a weakness to UNC's 3-2 drop zone, it's in the corners as a big man has to scramble out from the block when the ball swings to his side. With the 1-3-1, Paige set up on the backside with J.P. Tokoto at the point. Paige's speed allowed him to cover the entire baseline while both bigs set up in the three-man fence across the free throw line.
"We were trying to keep them up top instead of driving in and kicking out," McDonald said.
Not only did the 1-3-1 close Duke's penetration lanes, but the two defenders set up on the wings took away certain looks from long range.
"It took them out of their rhythm offensively," Paige said. "They were getting into a rhythm against our man-to-man defense and were starting to go to their strengths. But we switched it up a couple of times and were able to get rebounds out of it, too."
As with any new defensive scheme, there were occasional gaps on the perimeter. By then, however, the Blue Devils appeared to be fatigued. Duke missed 11 of its final 12 3-point attempts.
"I said before the game that we hoped to guard them, but we also would like for them to miss some shots," Williams said. "And I think it was a little bit of both."
In 2008, Williams instructed his players to switch all screens against the trigger-happy Blue Devils - a strategy that he had never employed throughout his career – and it worked. Duke missed 19 of its 29 3-point attempts in the 76-68 Tar Heel victory at Cameron Indoor.