The experience of Vermont appeared to be the final straw that forced Mike Krzyzewski to reconsider his preseason vision for how Duke would play this season.
Eight days ago, Duke's interior defense created the path of least resistance for a Vermont team that had won one game and lost to Bryant and Wagner yet somehow had the ball with a chance to win on the final possession at Cameron Indoor Stadium.
Vermont got there by scoring 19 baskets at the rim and 50 points in the paint. It was the most points per possession the Catamounts had scored against any opponent since the 2011-12 season.
And this was not just a fluky no-show against a team that the Blue Devils did not take seriously. It was a trend that was developing, in part, because of a decision Duke's coaches made in the preseason.
Krzyzewski entered this season with a roster that screamed for experimentation.
The Blue Devils' only true big man is Marshall Plumlee, and it's become clear at this point in his career that he's nothing more than a body to eat up a couple minutes here and there. Coach K's other "bigs" are Amile Jefferson and Josh Hairston. Jefferson is an athlete without a lot of skill. Hairston is undersized at 6'8", and his greatest attribute is his veteran smarts.
Without a real defensive presence inside that commanded playing time—like Mason Plumlee—Krzyzewski made a decision early on that he would experiment with an extreme small-ball lineup that included Jabari Parker at the 5 and Rodney Hood at the 4. Both are 6'8", so Duke wasn't sacrificing much in the way of height. That allowed Coach K to put more scorers and shooters on the floor instead of a non-scorer like Jefferson or Hairston.
In some ways, the experiment was working. Coach K played a lineup that included Parker at the 5 and Hood at the 4 for 14 minutes and six seconds in the opener when Duke put 111 points on Davidson.
But while Duke's offense, led by Parker, has been one of the most efficient in the country, the defense has been nowhere near as good as the other elite teams in the country.
And that lack of size inside appears to be the issue.
The Blue Devils rank 114th in Ken Pomeroy's adjusted defensive efficiency, and their field-goal percentage defense inside the arc (50.7 percent) ranks 220th, both of which would by far be the lowest ranking Coach K's teams have had since Pomeroy started tracking advanced statistics in the 2002-03 season.
Duke's defense at the rim has been so bad that it's been inviting. Kansas exploited Duke's small lineup by pounding the ball in the post at the Champions Classic in Chicago. Trying to get to the rim has been the copycat game plan for opponents since.
Opponents are attempting 38 percent of their shots at the rim and making 63.8 percent of those attempts, which ranks 272nd, according to Hoop-Math.com.
Whether it was a notion that Duke could just outscore teams or an unfamiliarity with how to protect the rim, something had to change.
And Coach K made that change last week in two games in New York.
Krzyzewski used the lineup with Hood and Parker inside for 15 minutes and 12 seconds against Vermont, including the final 11:18 of that game.
He used it much more sparingly in New York. Against Alabama, Hood and Parker were the inside duo for only 17 defensive possessions. Against Arizona, Coach K did not go to his extreme small-ball lineup until the final 2:18, when his team was trying to rally by scoring quickly.
Those lineup changes did not change the fact that Duke is still undersized, nor did they suddenly add a rim-protector. Parker is the only Blue Devil with more than three blocks, and Duke was definitely out-sized by Arizona's big front line.
What the Blue Devils did better in New York was force turnovers with their quickness. That was the plan in the preseason, but Duke had forced only 11.7 turnovers per game through six games. In New York, the Blue Devils forced more turnovers against both Alabama and Arizona—16 in each game—than they had all season.
The key to forcing those turnovers and protecting the rim was an increased focus on defensive rotations. Anytime Arizona tried to lob the ball into the post, Duke's guards swarmed in to help on the back side. In the picture below, Rodney Hood cheated off Aaron Gordon at the top of the screen. Hood arrived just as the ball got to Kaleb Tarczewski and was able to strip it away.
Because of their lack of size, the Blue Devils also needed to focus on not allowing drivers into the lane. Parker and Hood do a good job in this next play of double-teaming Nick Johnson as he dribbles off a ball screen. Rasheed Sulaimon then rotates from the help side to get a steal.
This is the type of rotation defense that Coach K had success with while coaching undersized lineups in the Olympics. No matter the lineups, this is how the Blue Devils have to play.
While the defense was better in New York, it wasn't all rosy.
The Wildcats still attempted 21 of their 47 field-goal attempts at the rim, and several of their baskets during a 24-8 second-half run that won the game came from getting to the rim with ease.
Look at Duke's help defenders when Aaron Gordon makes a drive to the basket. Not one Blue Devil stepped in to try to take a charge.
Taking charges has always been a staple of Coach K's defense, and it's possible that the new rules have made his guys gun-shy.
Krzyzewski even went to a zone late against Arizona to try to keep the ball out of the paint, something he said recently that he would not do. He probably regretted that decision as well, as the Blue Devils allowed two dunks on the first two possessions they went zone.
Even with those late-game lapses, progress was made in New York, and it's definitely way too early to say Coach K's group cannot improve. And "help is on the way" next season in the form of true big man Jahlil Okafor.
As for this season, it's obvious that the Blue Devils have to get much better on the defensive end in order to compete for the ACC title and go on a March run. At some point, they'll run into other teams with post scorers like Arizona and Kansas.
The answers appear to be improved rotations and forcing more turnovers, and Coach K finally appears willing to sacrifice playing his best offensive lineups to make that happen.
Follow C.J. on Twitter @cjmoore4.