The burgeoning irony of the 2017-18 Duke basketball season is that the Blue Devils earned their most significant victory to date with their defense.

That’s hard to figure.

They are the No. 104 defense in college basketball according to KenPom.com, which measures effectiveness by the number of points allowed per possession. They rank 76th in field goal defense and 244th in 3-point defense. Their three ACC opponents to date have averaged 92.7 points.

In the third game of the season, though, Michigan State was not prepared for the 2-3 zone Duke presented and committed 17 turnovers that were decisive in an 88-81 Blue Devils victory. The Spartans won their next 14 in a row and rose to No. 1 in the polls before an upset loss to Ohio State on Sunday.

Since that night, Duke found a way to compile a 13-2 record without really stopping anyone in its weight class. Major opponents are averaging 86 points against this defense. Some of that is a function of Duke preferring the fastest pace possible to maximize the impact of its extraordinary offensive capability. Some of it is not.

"We played young, which we are," coach Mike Krzyzewski said following the team’s 96-85 loss to N.C. State late Saturday. "They’re 18, 19 years old, but they’re playing against guys who have played. Have lost, have won, have been hurt — and we’re they’re opportunity. They’ve never experienced anything like that, where the team that you see on tape isn’t the team that shows up against you."

Duke operated a lot in the 2-3 zone against the Wolfpack, but it wasn’t effective, and when the Blue Devils switched to man-to-man, they struggled noticeably to defend pick-and-roll situations and also to rotate properly.

N.C. State shot 50.7 percent from the field and won even though it didn’t have an overwhelming edge in free throw attempts (only two more than the visitors) and didn’t connect on a substantial number of 3-point attempts (only 5-of-14).

Although he praised N.C. State effusively, Krzyzewski suggested some of the problem with the Devils was a schedule that had them play only three times since Dec. 9, which he said limited the ability to develop cohesion.

"We played crappy defense. We were frantic. They played their butts off. We’ve got to get better," Krzyzewski said following the game. "Now, the process of getting there, that’s what we have to figure out. For the most part, we’ve been able to do that. And hopefully we’ll be able to do that again.

"And if we don’t, then you’ll see us lose again. And you’ll ask if we’re working on our defense. And I’ll tell you that we are working on our defense, but it’s not working."

Duke starts four freshmen — all of them potential first-round draft picks — along with senior guard Grayson Allen. Although the team played Saturday without backup big man Marques Bolden because of a knee injury, the rotation is heavily weighted toward frontcourt players. There is no perimeter sub playing significant minutes since the Devils resumed ACC play in the FSU game.

In 2014-15, Duke also had an exceptionally gifted group of freshmen and struggled for much of the year to develop an effective defense even while compiling a 29-4 record and earning a No. 1 seed. When the NCAA Tournament began, the Devils ranked No. 57 in the nation in efficiency; no team since statistician Ken Pomeroy began tracking these numbers had ever won with such a porous defense.

Krzyzewski was able to make a lineup adjustment late in the season, though, inserting 6-7 Justise Winslow as power forward in place of 6-9 Amile Jefferson. The Devils became more dynamic. They surged all the way to No. 11 in the final defensive rankings and won the NCAA Championship by holding Wisconsin to 63 points and 41 percent shooting.

He doesn’t have a Winslow this time, so the guys he has will need to improve. That begins with better pressure against the basketball, whether the Devils are in man or zone; too often N.C. State was able to pass without any discouragement.

Big men Wendell Carter and Marvin Bagley have to improve their awareness of the basketball and of offensive intent, although Carter is blocking nearly two shots per game. With his length and experience, Allen should be a defender capable of impacting a game, but that doesn’t happen frequently enough. As a team, Duke gets only seven steals per game, which ranks outside the top 115 among Division I teams.

"Keep working. What answer would you want me to say?" Krzyzewski told a reporter. "It’s pretty simple. You try to keep getting better."