The buzz was building once again for Duke. The Blue Devils had tweaked their system, moving Grayson Allen to the point guard spot and playing zone defense on a more full-time basis. They won four in a row with Marvin Bagley III sidelined with an injury, then had their second-best defensive performance of the season in his first game back against Syracuse on Saturday.

The preseason favorite to cut down the nets in San Antonio had found itself back at the top of that discussion.

And just as everyone was about to buy into them again, Duke went to Blacksburg, Virginia, on Monday and fell to Virginia Tech, 64-63.

The Blue Devils made their last field goal with 7 minutes, 2 seconds remaining, scoring just five points the rest of the way. Virginia Tech ended the game on a 13-3 run -- including six straight points in the final 2:08.

It’s not the first time this season that Duke has looked like the best team in the country for a stretch, only to suffer a surprising loss and raise questions again. The Blue Devils rolled through the first month of the season, but they had defensive struggles despite the wins, and then dropped games to Boston College and NC State in a four-game span. They then won five in a row before losing three of four, including a game to St. John’s.

What has been holding Duke back from consistently being the nation’s best team?

The defense was an easy culprit the first few months of the season, but the Blue Devils’ switch to a zone defense has been an enormous boost, now sitting inside the top 20 in adjusted defensive efficiency. Before Monday’s game, Duke had held its previous five opponents to below one point per possession. Its effort at that end of the floor against Virginia Tech wasn’t bad, either, holding the Hokies to less than one point per possession and limiting them to 5-for-22 from behind the arc.

Getting Bagley readjusted into the “new” Duke -- Allen playing point guard -- could be something to watch. The Blue Devils have had their two worst offensive games of the season in the past two games, scoring 60 points against Syracuse and 63 against Virginia Tech. Virginia is the only other team to hold Duke to fewer than 65 points this season. Allen put up decent numbers on Monday, scoring 22 points and dishing out three assists, but shot just 6-for-18 from the field. In his previous three games that Bagley also played in, Allen averaged just 7.3 points.

Duke’s shooting has abandoned them in the past two games, shooting a combined 10-for-46 from behind the arc against Syracuse and Virginia Tech. Gary Trent Jr., who was on fire for most of January and February, is 2-for-13 in his past two games, while Allen is 4-for-21. When those two guys aren’t making shots, it allows defenses to focus more on Bagley and Wendell Carter Jr., and crowd the paint.

Maybe the biggest factor on Monday, though? Playing a team in Virginia Tech, on its home court, that knew a win would punch its ticket to the NCAA tournament. The Hokies were in decent shape heading into the week, sitting as a 10-seed in Joe Lunardi’s latest Bracketology. But they were also one of Lunardi’s “Last Four Byes,” meaning they were by no means a lock.

Now, Virginia Tech is undoubtedly dancing. Over the past 16 days, the Hokies have a win at Virginia and home wins over Clemson and Duke. Throw in a double-digit win over North Carolina in late January, and Virginia Tech has played like a top-25 team in the past month. It’s a stark contrast to the Hokies of the first two months of the season, which was essentially a nondescript group that had done nothing of note. The Hokies lost to Saint Louis on a neutral court in November, and their best nonconference wins were over Washington and Ole Miss. They then started 2-4 in ACC play. For a team with six juniors or seniors in its top eight, it was puzzling. But Tech began buying in defensively and Justin Robinson has developed into one of the best point guards in the ACC.

They’re now 8-3 in their past 11 games, and won’t have to sweat much on Selection Sunday.

Duke won’t be sweating, either. But the Blue Devils are likely out of the No. 1-seed discussion -- barring an ACC tournament title along with losses from Michigan State and Kansas. And now, after figuring out their defensive issues, they have to work out some kinks offensively.

Five weeks from today, a national champion will be crowned. Duke has the talent to get there, but Monday gave us another reason for pause.