As little as two weeks ago, Duke’s defense was porous. 

Flimsy. Torn to shreds. Even nonexistent. But oh, how the tide has turned.

Three games after switching to a zone defense, the No. 5 Blue Devils held their third straight ACC opponent to fewer than 60 points for the first time since 1981, extinguishing Louisville’s shooting almost entirely in an 82-56 win Wednesday at Cameron Indoor Stadium. Although Duke yielded a double-double to Cardinal forward Ray Spalding, it essentially neutralized Deng Adel and Quentin Snider on the perimeter.

In their last three games, the Blue Devils have held opponents to shoot just 28.3 percent from deep, a massive improvement for a Duke team that had struggled mightily to defend the perimeter at times earlier this season. 

“We don’t have as many perimeter guys. But we have length and we have fairly good lateral movement from each kid,” head coach Mike Krzyzewski said. “We talk better in the zone. We’re more unified in the zone.... And Grayson is able to lead us better. Instead of covering one person, you see him orchestrating things offensively and defensively.”

Without transcendent freshman Marvin Bagley III due to a knee sprain for the fourth straight game, Grayson Allen commanded the offense with 28 points on six 3-pointers. His triple midway through the first half sparked a 26-10 run to close the half, and the Blue Devils (23-5, 11-4 in the ACC) never looked back. 

It wasn’t always easy for the senior captain—he had to break through a deep dry spell that plagued him at the end of the first half. But he exploded for 13 points in a roughly six-minute stretch midway through the second that extinguished any of Louisville’s wildest lingering hopes. 

With Bagley out, Allen has scored 19-plus points in his last four games after getting snuffed out on offense for much of conference play. The senior has gotten far more looks—he took 20 shots—and has capitalized on them.

“I’m getting a lot of stuff not only off the ball, but off screens, coming down screens, then off the top with some ball screens, getting some stuff in transition where I can come off an attack and get stuff against defense that’s not set,” Allen said. “We’re doing a lot of really good stuff as a team and I’m able to get more open looks off of that.”

Even without Bagley and with center Marques Bolden playing through a nose fracture, Duke owned the defensive glass against a Louisville team (18-10, 8-7) that was one of the best in the nation in defensive rebounding before Wednesday. 

Sophomore Javin DeLaurier started for the Blue Devils and combined with Wendell Carter Jr. for a whopping 17 rebounds. Despite the fracture, Bolden did not wear any sort of protective gear on his face and ended up playing 16 minutes while scoring eight points and grabbing five rebounds. Bolden said that he tried wearing the mask, but it was just too much to play with. 

Although Bolden and DeLaurier have filled in well, Duke would still prefer to have Bagley back—Krzyzewski said he remains day-to-day with his knee injury. 

“Marvin has a problem, or else he would play. He’s getting better. It’s not a structural problem,” Krzyzewski said. “If we weren’t concerned about him having more injury, he would play. He’s not ready, but he’s getting closer now. I don’t know when it will happen. But I don’t want to push. You don’t want anyone out there who is thinking about a body part when you’re playing.”

Despite losing the battle on the glass in the very early going, Duke owned the paint for the bulk of the first half. The Blue Devils threw down seven dunks, including two putback slams from DeLaurier, to help break down a Cardinal defense that was one of the best in the nation at defending the hardwood inside the arc this year. 

Duke’s prowess inside the 3-point line helped it go on a 13-0 run midway through the first half that gave it a 20-point lead with just over two minutes left in the half. Although the Blue Devils were able to hold the Cardinals to shoot just 1-of-8 from deep in the first, they had difficulty at times keeping Louisville away from the rim.

Spalding and V.J. King combined for 20 of Louisville’s 25 first-half points, but Allen’s 13-point outburst and Duke's eight forced first-half turnovers were more than enough to negate it. 

Although Duke’s defense has improved steadily without Bagley in the lineup, Krzyzewski shot down concerns about reintegrating Bagley into the rotation once healthy. 

“We’ll handle that when that happens,” Krzyzewski said. “If Elton Brand came back or J.J. Redick came back, you [don’t say], 'Can’t play now. We’re playing too well.' We’ll figure it out. To win these four games without him is a really big-time thing. Javin, Marques, even Wendell, their confidence is higher.”

With the loss, the Cardinals have now dropped five of their last seven games. Duke will look to move its win streak to five games Saturday night at Cameron against Syracuse.