"He came in hot," Farrell said of the halftime pep talk Brey gave the team. "Kicking over things, throwing things. I can't repeat what he said, but he challenged us and we responded."
V.J. Beachem tied his career high with 22 points for the Irish (14-2, 3-0) who have won five straight.
Beachem, a New Haven High School alum, was coming off his worst game this season, a two-point effort against Louisville on Wednesday in which he only attempted three shots, but he had 11 points by halftime to keep the Irish within seven.
"Louisville did a really good job of chasing me everywhere and face-guarding me," Beachem said. "Clemson kind of lost me a little bit. I think that's why I was able to get some more open looks."
"If he's not going in the first half, we may be down 25," said Brey after his 700th game as a Division I head coach. "We were a mess."
Bonzie Colson recorded his ACC-best 10th double-double of the season with 13 points and 12 rebounds for Notre Dame and Steve Vasturia added 14 points.
"It's hard to guard them all," Clemson coach Brad Brownell said. "Beachem was a difference maker, he was outstanding in the first half."
Jaron Blossomgame had 22 points and eight rebounds for Clemson (11-4, 1-2) and Gabe DeVoe knocked down a career-high four 3-pointers, all in the first half, while scoring 14 points.
A steal by Elijah Thomas and his jump hook at the other end gave Clemson a 66-64 lead with 3:04 to play, but Farrell answered with a 3-pointer for Notre Dame.
Vasturia's 3 from the corner with 1:46 left put the Irish up by two, but Blossomgame's one-handed floater in the lane tied it at 70.
With a minute left, Colson tossed in a floater from the lane to give the Irish the lead for good.
Beachem hit two 3s in an 11-2 run early in the second half that gave the Irish a 46-45 advantage, as the lead changed hands 11 times in the second half.
"Beachem made some really tough shots," Brownell said. "That's what you get when you play Notre Dame. They just have so many weapons."
After Clemson scored the first 10 points of the game, Brey went to a four-guard lineup, and the Irish began to hit from deep. Their first six field goals were all 3-pointers and a 17-2 run gave them a five-point lead just over 9 minutes in. Notre Dame finished 15 of 32 from 3-point range.
"We didn't get off to a great start, but when it counted, we delivered," Brey said.
Clemson: With this outcome added to Tuesday's contentious loss to North Carolina, which stopped a nine-game winning streak for the Tigers, momentum is not on Clemson's side right now.
Notre Dame: On the other hand, the Irish are riding high with three ACC wins out of the gate, but now enter a seven-game stretch in the schedule through the end of January that features four teams currently ranked in the Top 25.
Late in the second half, the Irish were being outrebounded 33-22, but over the final 6 minutes they grabbed every loose ball and seven straight rebounds to end the game.
On defense, Notre Dame came up with three straight stops — what Brey calls a "kill" — over the final 1:25.
"Our will to win, not only today, but all week, has been fabulous," Brey said. "I thought our defense was a key again the last couple minutes to get enough stops."
With two impressive wins this week, including Wednesday's upset of No. 9 Louisville, Notre Dame could make a move into the top 20 come Monday.
Clemson: The Tigers head to Atlanta to play Georgia Tech on Thursday before returning home to face No. 11 Virginia next Saturday.
Notre Dame: The Irish travel to Miami on Thursday, kicking off a three-game trip that will also take them to No. 21 Virginia Tech and No. 12 Florida State.
More AP college basketball: www.collegebasketball.ap.org and https://twitter.com/AP_Top25.