Before Friday’s NCAA regional semifinal against the Gophers, Oregon’s players made themselves a promise. Facing the No. 2 seed in the tournament, in a gym where the Gophers had lost only twice in four years, the Ducks realized there was only one way to approach things.

“We decided at the beginning that no matter what, we were going to be fearless in everything we did,” setter August Raskie said. “Just play with no fear.”

Their stout hearts — and a brilliant game plan, executed to perfection — carried the 15th-seeded Ducks to a monumental upset. They won 21-25, 41-39, 25-14, 26-24 at Maturi Pavilion, dashing the Gophers’ dream of playing for an NCAA volleyball championship next weekend at Target Center. The Sweet 16 victory vaulted Oregon into the regional final against Nebraska and brought a sudden, stunning end to one of the Gophers’ best seasons ever.

The match turned on that marathon second set. The Gophers thought they had won it 39-37 when Samantha Seliger-Swenson appeared to slide her flattened hand under a ball, keeping it aloft for an Alexis Hart kill. Oregon coach Matt Ulmer challenged the call, saying the ball had hit the floor, and a reversal of the point dealt the Gophers an emotional blow they could not shake.

The Ducks (23-10) will face defending national champion Nebraska, a 3-0 winner over Kentucky in Friday’s earlier semifinal, Saturday at Maturi Pavilion. The winner advances to the Final Four.

The Gophers ended the season with a 27-4 record, with two of those losses coming to Oregon.

“It’s disappointing, for a lot of reasons,” Gophers coach Hugh McCutcheon said. “This group worked incredibly hard, and I felt they deserved the chance to compete at the end of this thing.

“But that’s not going to be our lot in life. So we’ve got to deal with what is, and we’ll move on.”

Oregon, which beat the Gophers 3-1 on Sept. 7 in Stanford, Calif., kept them scrambling with a hard-to-read offense and disciplined defense. Its pinpoint passing and fast pace spread the Gophers out, creating spaces for its hitters to bury kills. The Gophers also struggled to hit over the Ducks’ block in the second half of the match.

One of the nation’s most accurate teams, the Gophers hit progressively worse as the match went on. They finished with a .260 hitting percentage — including .111 or below in the final two sets — while Oregon hit .313. The Ducks topped the Gophers in kills (82-71), digs (94-86) and blocks (11-8).

“Winning the second set was important for us,” Ulmer said. “I think [the Gophers] had a hard time responding to that. Then we just got a little bit more confident, the crowd got a little bit quieter, and we just kept going.”

The Ducks’ fearlessness started early. With a 10-3 record on the road this season, Oregon middle blocker Ronika Stone said her team actually felt it was an advantage to play away from home, despite the Gophers’ 16-0 record this season at Maturi Pavilion.

An announced crowd of 5,187 fueled the Gophers in the first set, when they used their usual formula — a balanced, accurate attack — to outlast the Ducks. The Gophers hit .465 in that set before the Ducks got locked into their plan.

The seesaw second set featured 26 ties, 11 lead changes, four coach’s challenges and 17 set points. After Seliger-Swenson’s apparent dig — and Hart’s smash — the Gophers celebrated and headed off the floor. But the point was reversed, and following the Gophers’ ninth foiled set point, Oregon’s Brooke Van Sickle ended it with two kills.

“We got our hearts broken a little bit,” McCutcheon said. “It took us a while to recover.”

Oregon led by as many as 10 points in the third set. The 14 points were the fewest for the Gophers in any set this season.

Asked how his team would make the quick turnaround for Saturday’s match, Ulmer laughed.

“It’s going to be a train wreck,” he said, knowing the adrenaline-charged Ducks would likely be awake past midnight. “It was a super emotional match in every aspect.”

The Gophers could relate, in a much different way.

“I think it’s still a phenomenal season for us, even if it’s not the end that all of us wanted,” McCutcheon said. “Sometimes, when you compete for a living, it doesn’t work out the way you want.”