Duke’s Cam Reddish sinks a three-pointer over Virginia’s Kyle Guy on Saturday in Charlottesville. The No. 2 Blue Devils made 13 of 21 three-point attempts in an 81-71 win over the No. 3 Cavaliers. (John McDonnell/The Washington Post)

Long regarded as the most unforgiving defense in the country under Coach Tony Bennett, the Virginia men’s basketball team’s “pack line” wilted trying to guard No. 2 Duke on Saturday evening.

In allowing their most points this season, the Cavaliers were particularly spotty challenging shots from beyond the arc, with the Blue Devils making 13 of 21 while rolling to an 81-71 win. Duke swept the regular season series and dropped Virginia into second place in the ACC.

It was the most three-pointers Virginia (20-2, 8-2) has permitted this season. Its previous high was eight to Notre Dame on 29 attempts. The Cavaliers entered the highly anticipated showdown leading the country in three-point field goal shooting defense, allowing just 24.7 percent.

“I thought we were a little slow to our closeouts,” said Virginia Coach Tony Bennett, who has a winning record against every ACC opponent except Duke. “We tried to keep them out of the lane and jam the lane, and we probably overcorrected in terms of that.”

RJ Barrett did most of the offensive damage for Duke (21-2, 9-1), making a season-high 6 of 10 from beyond the arc to finish with a game-high 26 points and end Virginia’s 13-game home winning streak. Zion Williamson added 18 points, making 6 of 8 field goal attempts.

Duke shot 57.8 percent overall — the highest by a Virginia opponent — in winning its seventh in a row to remain in a first-place tie in the conference with No. 8 North Carolina, which hosts the Cavaliers on Monday night.

Kyle Guy led Virginia with 16 points but committed five of the Cavaliers’ 14 turnovers. Virginia has 44 turnovers over its past three games despite coming in first nationally in fewest turnovers (9.0).

Ty Jerome, who missed the Cavaliers’ last game with a sore back, also had 16 points.

The closest the Cavaliers came down the stretch was 66-61 with 5:25 left in the second half, but Duke reeled off six in a row to all but seal the outcome in front of an announced crowd of 14,629 that included LeBron James and Rajon Rondo, whose Los Angeles Lakers face the Philadelphia 76ers at Wells Fargo Center on Sunday.

Also in attendance at John Paul Jones Arena was former Duke star Grant Hill.

“They’re just a good team, and we did what our principles tell us to do,” Guy said. “We did a much better job in the gap, and they didn’t get as many driving lanes, but when you hit 13 threes, you’re going to be hard to beat.”

Center Jay Huff came off the bench to provide a lift for the Cavaliers early in the second half. The 7-foot-1 redshirt sophomore made a three-pointer and delivered a pass into a tight window to Braxton Key for a layup that trimmed the deficit to 54-49 with 12:19 to play.

But as had been the case in the first half, just when Virginia had been gaining steam, the Blue Devils answered with a timely three-pointer, this time from staring point guard Tre Jones from the left corner. Jones added two free throws not long after, and Duke led 59-49.

“Whenever they kind of had a run, one of our guys answered,” Duke Coach Mike Krzyzewski said. “It was really kind of neat to see the kids step up that way. Not one guy, but they kind of took turns doing it, like a counterpunch.”

The momentum of Virginia’s rousing finish to the first half failed to carry over coming out of the locker room. The Blue Devils instead expanded their lead to 52-41 on the strength of three three-pointers from Cam Reddish as part of an 11-4 push, leading to a timeout by Bennett.

The rematch between teams with national championship aspirations came three weeks after the Blue Devils held off Virginia at Cameron Indoor Stadium for a 72-70 win, the most points the Cavaliers had allowed this season until Saturday.

Duke played that game without Jones, who sat with a shoulder injury.

Indicative of Jones’s defensive value to the Blue Devils, their steal percentage dropped to 6 percent without him. With Jones in the lineup, Duke leads the country in steal percentage (13.9). He also leads the ACC in assists (5.5) and assist-to-turnover ratio (4.8).

The Cavaliers, meanwhile, had been dealing with uncertainty surrounding their starting point guard in Jerome. The junior was unavailable for the Feb. 2 game against Miami, the first time he has sat out in his career — a span of 89 games.

Bennett didn’t hold practice Sunday and Monday for rest and recovery and indicated Jerome was moving the in the right direction with regard to his sore back he initially tweaked on Jan. 29 in the early portion of a 66-65 overtime win against North Carolina State in Raleigh.

“I didn’t know for sure until about Thursday that I was going to play,” Jerome said. “I practiced off and on all week, and I practiced pretty much the whole time on Friday, and I felt all right.”

Jerome had two field goals in the first half and didn’t appear bothered by his back, but it was Guy who rose up in the final minutes to help Virginia claw back from a 14-point deficit to trail 39-35 at halftime even though the Blue Devils, ranked 13th in the ACC in three-point shooting, went 8 for 11 from beyond the arc.

The first half also included a head-to-head collision between De’Andre Hunter and Mamadi Diakite that sent Diakite, a starting forward, tumbling to the court along the baseline by the Duke bench.

It’s unclear, according to Bennett, whether Diakite will be available against the Tar Heels.

“It was a big loss,” Hunter said of Diakite, who had seven points on 3-for-4 shooting. “He was playing really well. We didn’t know whether he was going to play or not, but it was definitely a big loss.”