Virginia Teach’s Justin Robinson drives to the basket against Notre Dame during the second half of the Irish’s 71-65 win over the Hokies at Barclays Center in the ACC tournament. (Abbie Parr/Getty Images)

Not even a 21-point lead in the second half proved enough for Virginia Tech to avoid a stunning collapse against Notre Dame.

That the 71-65 loss unfolded in the second round of the ACC tournament had the seventh-seeded Hokies (21-11) smarting all the more, leaving players and Coach Buzz Williams heading back to Blacksburg, Va., with their NCAA tournament seeding almost certain to suffer on the heels of the early exit at Barclays Center.

The No. 10 seed Fighting Irish (20-13), meanwhile, continued to make the case that they belong in the field of 68 thanks to a fourth win in five games with standout forward Bonzie Colson back in the lineup after an injury that kept him out for much of the season.

Notre Dame, which faces second-seeded Duke in Thursday’s quarterfinals, went ahead for good at 60-59 with 2:02 left in the second half on Colson’s three-pointer off the glass with the shot clock expiring. The Fighting Irish made 11 of 14 free throws down the stretch to complete a rally after trailing 47-26 with 15:07 to play.

“Just fell apart in the last 15 minutes defensively,” Williams said. “You can point to a lot of things. Offense wasn’t great. They started switching everything just to try to keep us in front, rightfully so. I thought we had done a good job up until that point through the first 25 minutes.”

While Notre Dame was forging its comeback, the Hokies went 1 for 13 from the field and scoreless for more than seven minutes in losing for the third time in four games.

It also was the third game in that span in which they failed to protect a double-digit lead. Virginia Tech lost to Louisville, 75-68, at Cassell Coliseum on Feb. 24 after leading by 10 in the first half and at Miami, 69-68, on Saturday after it was up by 12 late in the first half.

Guard Justin Robinson and forward Justin Bibbs each scored 15 points for the Hokies, who were unable to advance despite holding a 17-2 margin in bench points and 30-16 on points in the paint.

Reserve forward Chris Clarke added 12 points and was assessed a technical foul with eight minutes left that, according to Fighting Irish guard Matt Farrell, sparked Notre Dame. Farrell and Clarke bumped into one another after the whistle, and Farrell fell into a group of photographers on the baseline, drawing the whistle.

“It kind of got us going,” Farrell said. “Guys had more energy in the huddle. We showed a little toughness. We’ve got to start games like that. We’ve got to show toughness right away like that, but I think for sure it shifted momentum.”

Farrell had a game-high 22 points, 17 of which came in the second half when Coach Mike Brey made the decision to move the senior off the ball and turn point guard duties over to T.J. Gibbs Jr.

That tactical switch allowed Farrell to get cleaner looks at the basket, and Notre Dame capitalized overall by making 7 of 13 three-point attempts in the second half.

The Hokies had limited one of the ACC’s most efficient three-point shooting teams when healthy to 3 for 16 from beyond the arc in the first half.

“Like Coach said, we just fell apart,” Robinson said. “I mean, it’s a learning experience. Hopefully we take positives and negatives from it and just move on from it.”

Virginia Tech led 34-21 at halftime, holding Colson to 1-for-10 shooting. The preseason all-American missed multiple shots within several feet of the rim as he played in back-to-back games for the first time this season.

The Hokies appeared well on their way to a comfortable result when they got a three-point play from forward Kerry Blackshear Jr. for a 41-23 lead with 16:59 left in regulation. They extended the margin to 21 with three consecutive layups before the Fighting Irish began their uprising.

To reach the second round, Notre Dame held on against Pittsburgh, 67-64, on Tuesday behind Colson’s 19 points, six rebounds and three blocks. Colson had 12 against the Hokies on Wednesday.

The injury kept Colson out for 15 games, during which time the Fighting Irish went 6-9, including an 80-75 loss to Virginia Tech on Jan. 27 in South Bend, Ind., to remain on the fringe of NCAA tournament inclusion.

“You know, I’ve never been a big guy to campaign, but I think we really deserve to be in,” Brey said. “And I don’t want to hear about the best 68. When I have my guys back, we’re a top 20 team, and I think the people in that committee know that. I feel strongly that we should be a part of it.”