DURHAM, N.C. — Normally, a fifth win in six games would sound far different.

More jovial. More encouraged. More befitting of a team that just moved to 15-1 on the season, 4-0 in the ACC and remains a verified national title contender.

But one of Jon Scheyer’s best attributes, even when things appear to be going well, is transparency. Telling things like they are.

And after No. 6 Duke’s 82-75 win over No. 24 SMU on Saturday — its sixth win over a ranked opponent — the Blue Devils’ fourth-year head coach wasn’t going to talk around the elephant in the room: his once-vaunted defense has been nowhere near good enough for most of the last month.

“It’s been an issue,” Scheyer said.

Imagine saying that at any previous point in Scheyer’s tenure as head coach. Scheyer learned firsthand from Mike Krzyzewski — first as a player, then as an assistant — that defense wins championships, and reaffirmed that as the tentpole of the program the last three seasons. Duke finished 16th nationally in adjusted defensive efficiency, per KenPom, in each of Scheyer’s first two seasons before last year’s Final Four team finished fifth in the country.

And while Duke still ranks 10th in the country in adjusted defensive efficiency even after Saturday — when it allowed SMU (12-4, 1-2), down its leading scorer Boopie Miller, to shoot 56.6 percent overall and 50 percent from 3 — that doesn’t tell the full story.

“Collectively, it’s not there at the moment,” Scheyer said. “It’s hard to feel very good when they shoot 56 percent from the field all game.”

The thing that must be difficult for Scheyer to square is that earlier this season, Duke did flex elite defensive potential. But the Blue Devils’ first 10 games this season, and their last six — dating back to the Lipscomb game on Dec. 16 — have looked like two totally different teams:

First 10 games

Last 5 games (entering SMU)

Difference

Defensive effective FG%

40%

56.40%

16.40%

Defensive effective FG% rank

1st

307th

2-point defense

39.90%

55.80%

16.90%

2-point defensive rank

2nd

283rd

3-point defense

26.70%

38.20%

11.50%

3-point defensive rank

7th

289th

“There’s obviously things we’ve got to clean up and do better,” Scheyer said. “To me, it’s mentality, and then obviously there’s some X’s and O’s strategic things that we’ve gotta help them with as coaches.”

About that second point. While Duke, like most college basketball teams, changes its defensive coverages depending on matchups, Scheyer’s defensive trump card through his first three seasons has been undeniable: the ability to switch one through five.