The second-seeded Buckeyes, who had won 10 straight conference tournament games, saw an early 13-point lead fade completely away late in the first half. Then they watched the sixth seed surge to as much as a 19-point advantage early in the second half to win comfortably.
Ohio State built a 21-8 lead as Nebraska struggled to find the range from anywhere for the first 13 minutes of the first half, but the Cornhuskers caught fire and caught the Buckeyes at 24.
Nebraska went ahead 27-24 on a Kaitlyn Burke three-pointer with under three minutes left in the half. Samantha Prahalis answered with a jumper in the lane that brought a 13-0 Nebraska run to an end, but the Cornhuskers weren't done.
Nebraska forward Jordan Hooper came back with another wide-open trey from the top of the key, and Brandi Jeffery added a layup when she blew past 6-5 Ohio State center Ashley Adams off the dribble.
On the next trip down the floor, Prahalis picked up a technical foul arguing she had been bumped on a layup, and the Huskers took advantage of the call by making both free throws and adding a layup to push their lead to eight points.
Prahalis answered with another layup to close the scoring and send the teams to the Buckeyes to the locker room down 36-30.
After starting 2 for 21 from the floor, Nebraska made nine field goals in a row, a streak that only ended when Hooper missed a long heave as the half wound down.
In the second half the Huskers picked up where they left off, starting on a 12-2 run to expand their lead to 48-32 with 16 minutes left in the game.
Ohio State head coach Jim Foster felt the Buckeyes helped jump-start the Husker comeback with fouls in the first half.
"Now are going to the foul line when they are struggling to score points," Foster said.
"When you're that energetic, you've got to be disciplined. You've got to be in the right place at the right time. And then I think when we started to commit the fouls, I think we backed off our pressure. And they could run their offense much more efficiently, because the pressure that was causing them a lot of problems early was not as significant."
Ohio State (25-6) showed some life on offense five minutes into the second half but could not come up with defensive stops to cut into the lead. It peaked at 19 on a Hailie Sample layup that made it 66-47 with 6:26 to play.
Prahalis finished with a game-high 23 points while fellow guard Tayler Hill added 10, but both struggled to create and make shots from the field. Prahalis was 7 for 18 on field goals, including 1 for 5 from three-point range, while Hill went 4 for 16 overall and missed all six of her trey attempts.
The Buckeyes were never in synch offensively and finished the game 25 for 61 (41 percent) from the floor and 2 for 16 (12.5 percent) from three-point range. They had 10 assists and committed 14 turnovers.
"I think we rushed and took low-percentage/high-difficulty kind of shots," Foster said. "One of the strengths of this team is the patience on offense, and we didn't play with that. And when you hurry like that against a team that's as potent as they are, it causes you problems. There's nothing they were doing to make us play fast. We were just playing fast."
While the veterans struggled, freshman Raven Ferguson came off the bench to provide a life with a career-high 13 points in 19 minutes.
Hooper led Nebraska with 21 points while Burke added 20 that head coach Connie Yori considered important because Ohio State focused its defensive efforts on Hooper, point guard Lindsey Moore and forward Emily Cady.
"They chose to guard Lindsey hard and Jordan and Emily hard and that enabled other kids to have looks," Yori said. "That's why Kaitlyn had the game she had. And somebody had to step up and make shots."
Moore had eight points and seven assists while Cady had 10 points and six steals.
"I think (Burke) played a very good game," Foster said. "She played like a senior who wanted it, played with a lot of poise. And I think her poise and her decision-making helped them a lot. I thought we were doing a very good job on those three players, but to her credit she stepped up."