Sometimes so much is decided by one slight bounce of the puck.

So it was Saturday night when Providence College staged a furious late-game comeback with help from one of the flukiest plays in Frozen Four history.

Ahead 3-2 midway in the third period, disaster struck for BU and their goaltender Matt O’Connor when a 100-foot knuckleball dressed in black was sent from center ice by Friars’ Kyle McKenzie on a routine shift change. A routine catch by O’Connor a thousand times. But this time he dropped it — and lost it as it dribbled over the goal line at 11:24 to tie the game at 3-3.

“I couldn’t really see it in my glove,” O’Connor said after. “I thought it rolled out of it. I tried to drop and throw it to Jack [Eichel] and it was too late.”

“He’s really been the backbone of our team all year,” BU captain Matt Grzelcyk said about O’Connor. “And I think every guy in the room would agree we wouldn’t be in the championship game without him.”

BU coach David Quinn immediately called a timeout.

“We were tired,” Quinn said about that decision, “and [I] just wanted to get Eichel’s line back out there and just kind of settle us down a little bit. There was nothing that needed to be said to Matt. Talked to the whole team including Matt, talked about what we needed to do to win the last seven, six minutes, whatever was left. They make a bang-bang play off the faceoffs.”

For the winning goal when Brandon Tanev took a faceoff pass from Canton’s Kevin Rooney two minutes later to payday, firing a 10-footer past BU’s beleaguered goaltender at 13:43 for the Friar lead.

Then it was all up to PC’s outstanding netminder, Jon Gillies, to hold the fort for Providence’s first national championship in school history, and the third in a row by first-time champions with Yale and Union winning it, respectively, the past two seasons.

The highly touted Gillies, a Calgary Flames draft pick with a 1.98 GAA did all of that, ending as the Most Outstanding Player with 49 saves on 52 shots Saturday night.

“He was big time for us,” fourth-year Providence coach Nate Leaman said postgame about Gillies’ performance. “He held the ship. He held us in there. And then we were able to kind of respond in the third period there. But he was our best player tonight.”

On one bench, the most remarkable turnaround in NCAA history with Boston University going from just 10 wins last season to the national championship game.

On the other, Providence College, the very last team to make the 16-team 2015 NCAA Tournament by .001 of a point in the Pairwise rankings — and a program that has never won it all.

It was also the first all-Hockey East final game with Boston as the host city.

The revamped BU roster took the league’s regular-season and tournament titles, skating eight freshmen, led by Hobey Baker winner Jack Eichel who led the nation in scoring and is a certain bet to be taken at No. 1 or No. 2 in June’s Entry Draft.

Providence featured 14 upperclassmen.

“We’re the youngest team in the country,” Quinn said. “We have four 18-year-old defensemen playing in the game tonight. We’ve got eight freshmen in the lineup. Sometimes experience is the best remedy for situations that we were in tonight.”

Sophomore Anthony Florentino drilled a 20-footer from the top of the right circle past O’Connor for the early — and temporary — 1-0 lead 9:25 into the game. BU countered with the two fastest goals in NCAA history when Finnish native Ahti Oksanen and Needham’s Danny O’Regan put BU up 2-1 at 12:50 and 12:54.

BU outshot Providence, 18-6 in the first period.

Providence pulled even at 4:29 of the second period with four seconds left on a power play. O’Connor stopped three point-blank shots before junior Mark Jankowski, a No. 1 draft pick also of the Flames, rifled one to twine.

At 11:36, Cason Hohmann put BU back in front when Oksanen pulled the puck out of a faceoff scrum and sent it to his center for a smooth 10-foot wrist shot past Gillies.

Twenty minutes left in the game. Twenty left for Providence to snatch victory. Twenty for BU to win their sixth national championship.

It wasn’t meant to be.

Hohmann had an open net with a minute to go, but his backhand was gobbled up by Gillies lunging back as BU pulled O’Connor for the frantic finish, throwing all they had at the 6-foot-5 Gillies.

“There’s a six-on-five,” Gillies said about the longest minute of his playing career, “so there’s a lot of traffic in front. Try and battle for the guys that are battling for you in front.”

The 67th Frozen Four will go down as one of the classic battles of all time, especially having been played in Boston between two local and storied programs.

“There’s not much I can say to make our guys feel any better or make anybody associated with BU hockey feel any better right now, but it’s been an incredible year,” Quinn said, “One team wins the last game of the season.”

“I thought it was a little bit like our season,” Leaman summed. “We started a little bit slow but we got better and better. And we played — we played a pretty good third period, and obviously got a big bounce. We’re fortunate enough to be a Catholic school where they say a lot of prayers.”

The All-Tournament Team consisted of forwards Jack Eichel, (BU), Mark Jankowski, (PC) and Ahti Oksanen, (BU); defensemen Matt Grzelcyk, (BU) and Anthony Florentino, (PC), and Providence’s Gillies, the most outstanding player.

(Bob Snow has covered the Frozen Four since 1998.)