Denver forward Kohen Olischefski (12) celebrates his goal during the first period in the semifinals of the Frozen Four NCAA men’s college hockey tournament against Massachusetts on Thursday, April 11, 2019, in Buffalo, N.Y. (AP Photo/Jeffrey T. Barnes)

BUFFALO, N.Y. | Marc Del Gaizo was still having difficulty putting into perspective the role he played in helping Massachusetts advance to college hockey’s Frozen Four championship game for the first time in school history.

“It’s probably the coolest moment of my life,” the freshman defenseman said. “Right now it seems like I’m dreaming, but we’re off to the national championship and that’s all that matters.”

Del Gaizo scored 15:18 into overtime to seal a 4-3 victory over Denver in a semifinal game that ended in just after midnight Friday.

The Minutemen (31-9), making just their second NCAA Tournament appearance, rebounded after squandering a 3-1, third-period lead and overcome having two forwards — including captain Niko Hildenbrand — ejected for illegal hits to the head.

Mitchell Chaffee, John Leonard and Bobby Trivigno also scored and Jacob Pritchard had two assists to extend a transformational season in which UMass already eclipsed its program-best victory total of 21.

Filip Lindberg, coming off consecutive shutouts in the first two rounds, stopped 37 shots. His best save of overtime came a little over eight minutes in when he got across to his left to stop Tyson McLellan, who got off a backhander from in close.

The Minutemen will face defending champion Minnesota Duluth in the championship game Saturday. The Bulldogs (28-11-2) advanced to their third consecutive championship with a 4-1 win over Providence.

The Pioneers (24-12-5) were denied an opportunity to make their 11th championship game appearance and a shot to win their ninth title, and second since 2017.

Freshman forward Cole Guttman scored twice in less than six minutes in the third period to force overtime. Colin Staub also scored for Denver. Filip Larsson, who was also coming off consecutive shutouts, finished with 23 saves.

“We thought we were winning the game,” Staub said. “We though we battled back, we were resilient, and there was no doubt in our minds going into that overtime.”

UMass refused to wilt.

“This team all year long, they’ve impressed everybody and tonight was just the next chapter of how resilient they are,” Minutemen coach Greg Carvel said.

Del Gaizo sealed the win when Oliver Chau dug out a loose puck behind Denver’s net and fed a pass into the left circle. Gaizo one-timed the shot that beat Larsson inside the far post.

“I’m not a guy known for my one-timer, but ‘Chausy’ just put it on a tee with me there,” Del Gaizo said. “It was a perfect pass, right in my wheelhouse, perfect speed, so I just got a hold of it and it went in.”

The game was marred by questionable checks, which resulted in Chaffee, Hildenbrand, and Denver’s Ryan Barrow being ejected for illegal hits.

The Minutemen were running out of gas in missing two top forwards as the game progressed. They were being outshot 11-3 in the third period when Guttman tied it, and 35-21 through three periods.

Guttman cut UMass’ lead to 3-2 by snapping a shot through a crowd and into the top left corner with 9:28 left. He then tied the game with 3:46 left, when he was alone in front to tap in McLellan’s pass from the right corner.

The head-contact penalties, which resulted in 5-minute majors, played a key role in the outcome.

Denver opened the scoring a little over two minutes after Hildenbrand was ejected 6:24 into the game, when he went high in checking Denver’s Tyson McLellan. Staub scored during a wild scramble in front, during which he was lying face down near the crease, where he swept his stick and chipped a loose puck just above Lindberg’s glove.

The Minutemen responded by scoring three power-play goals in a span of 2:31.

Trivigno tied the game at the 11:41 mark by tipping in Pritchard’s shot from the right circle with McLellan serving a holding penalty.

Then it was Barrow’s turn to be ejected for hitting Del Gaizo in the head during a mid-ice collision with 7:28 left in the first period. Chaffee scored 32 seconds later, when a pretty passing play left him wide open in the slot.

Leonard put the Minutemen up 3-1 when defenseman Cale Makar stopped a clearing attempt at the left point. He then fed Leonard, who stopped the pass with his skate and snapped a shot from the slot into the top right corner.

Chaffee was ejected with 3:48 left in the second period. Denver’s Ian Mitchell was cutting through the neutral zone when he was struck in the side of the head by Chaffee’s right shoulder.

NOTES: UMass was 0-3 against Denver, including a 5-3 loss in its last meeting, Dec. 17, 2013. … Makar’s assist upped his season total to 49 points, one short of the nation’s leaders, Penn State’s Alex Limoges and Michigan State’s Taro Hirose. No defenseman has ever led the NCAA in points. … The Pioneers had six players left from their 2017 championship team.