What does turbulent weekend mean for the ACC?

North Carolina’s Kennedy Meeks (3) drives to the basket against Georgia Tech’s Josh Okogie (5) during the first half on Saturday, Dec. 31, 2016, at McCamish Pavillion in Atlanta. Georgia Tech won, 75-63. (Robert Willett/Raleigh News & Observer/TNS)

North Carolina’s Kennedy Meeks (3) drives to the basket against Georgia Tech’s Josh Okogie (5) during the first half on Saturday, Dec. 31, 2016, at McCamish Pavillion in Atlanta. Georgia Tech won, 75-63. (Robert Willett/Raleigh News & Observer/TNS)

An ACC season that got off to an unlikely start took another sharp turn Monday. Georgia Tech is in the middle of the proceedings.

Duke coach Mike Krzyzewski will take a leave of absence after he undergoes surgery Friday on his lower back, adding another layer of uncertainty to the No. 8 Blue Devils and more broadly to the ACC. Tech, which stunned then-No. 9 North Carolina 75-63 on Saturday, will play Duke in Durham, N.C., on Wednesday.

Krzyzewski could be out for up to four weeks, according to the school. Krzyzewski is expected to coach against the Jackets before leaving the team in the hands of associate head coach Jeff Capel.

Duke began the season as the near-unanimous preseason No. 1 and was the heavy favorite to win the ACC with returning All-American guard Grayson Allen (voted ACC preseason player of the year) and a freshman class boasting three of the top 10 prospects in the country, according to ESPN’s rankings.

However, Allen was indefinitely suspended Dec. 22 after he tripped an opponent for the third time in less than a year, and the Blue Devils have been hit hard by injuries. They lost Saturday to Virginia Tech to drop to 12-2.

“Without Grayson Allen, Duke’s a little bit dysfunctional right now,” former Virginia Tech coach and ESPN analyst Seth Greenberg told the AJC on Monday. “I don’t think the pieces fit. You have a lot of talented players, but it doesn’t look like they have the same chemistry and trust that you expect from a Duke team.”

Duke and North Carolina both losing ACC openers is unusual. It was just the second time in the past 22 seasons that the two powerhouses both lost in their first game in league play. For good measure, Boston College, which was 0-18 in the ACC last season and picked to finish last this season, hammered Syracuse 96-81 on Sunday.

“We also know it’s a long season, a long haul, but great for Georgia Tech, great for the program,” Tech coach Josh Pastner said Monday. “Hey, we’re sitting here in 2017 in January first place in the ACC.”

Tech guard Josh Heath knows it. Heath scored 15 points, including a big 3-pointer, off the bench in the win over the Tar Heels. He was in Boston College’s corner Sunday. His father, Stan, is an assistant coach for the Eagles.

“There’s a lot of good players, a lot of good teams,” Heath said. “Anybody can beat anybody on any given day. You’ve got to bring the energy.”

On a scale of 1-10, Greenberg rated his surprise over Tech’s win a 9 or a 10. The website teamrankings.com gave Tech a 4.6 percent probability of winning. The rate that likely did not take consideration that the Tar Heels, while on the road, were playing in front of a McCamish Pavilion crowd heavily supporting the visitors, as many Tech fans were watching the football team’s bowl game, being played concurrently.

“You’ve got to be tough to beat Carolina,” Greenberg said. “It’s a testament to Josh (Pastner) and his staff that they got those kids to believe and trust each other.”

The loss by the Tar Heels, who saw the end of seven-game winning streak over Tech (games that had been won by an average of 17.4 points), was indeed mystifying.

“They have their excuses and explanations like the other two examples, but I still find that loss out of the three by far the most surprising,” said David Glenn, a longtime ACC observer and the host of a popular radio show in North Carolina.

Moreover, then-No. 20 Florida State beat then-No. 12 Virginia in Charlottesville, Va., where the Cavaliers had won 35 of their past 36 ACC home games.

But, the biggest development may be the absence of Krzyzewski. It is reminiscent of the leave of absence that he took in the 1994-95 season after having back surgery before the start of the season. Assistant coach Pete Gaudet coached the final 19 games of the season — his first was against Tech, coincidentally — with the Blue Devils going 4-15 in them and finishing 13-18. That was the most recent season in which Duke missed the NCAA tournament.

“One of the big differences was that (1994-95 team) was one of Mike Krzyzewski’s least talented teams of the last 30 years, and this (team), when healthy, is one of his most talented if it gets healthy, and it hasn’t really been that,” Glenn said. “But it complicates the journey a little bit.”

Glenn’s perception is that Krzyzewski trusts probably six players, and one of them is Allen, whose return date is unclear. Against Virginia Tech, four Duke starters played 37 minutes or more and only one sub played more than six minutes.

There was another notable piece of news Monday. Seven teams — Duke, Louisville, Virginia, Florida State, North Carolina, Virginia Tech and Notre Dame — made the latest AP Top 25.

“What happened this weekend speaks volumes to the season that we’re going to have, in that the bluebloods are back, but they’ve still got to play well and with that mentality,” Greenberg said.