The fifth-seeded Cowgirls (14-7-0, 7-5-0) will play the winner of the Texas-Texas A&M semifinal that will be played later Friday.
The final is 1 p.m. Sunday at Blossom Soccer Stadium.
Niemeier’s goal was set up when Kasey Langdon and Kyndall Treadwell moved the ball through the goal box, where Niemeier was waiting on the other side.
“I got a little lucky that the defender didn’t get it and it went through,” Niemeier said.
Niemeier leads the team with 11 goals. She has scored a point in seven-straight games and goals in six of the last seven.
It hasn’t always been that good. In a September loss to the Tigers at Columbia, Mizzou lost a 2-0 lead before going back ahead 3-2. Niemeier, a junior midfielder from Willingen-Ussein, Germany, had a chance to tie with a penalty kick that Tigers goalkeeper Tasha Dittamore stopped with seven minutes left.
“This is better,” Niemeier said.
The Tigers (13-6-3, 8-2-2) fell behind 1-0 in the first half Friday, but pulled even with a header from Alysha Bonnick in the 70th minute. Missouri pulled ahead 2-1 on Kristin Andrighetto’s free kick just outside the penalty box in the 75th minute.
Andrighetto had two goals, including the game-winner, in an overtime victory over Kansas in the quarterfinals Wednesday.
But OSU had a chance to respond. Only a minute later, the Cowgirls’ Siera Strawser scored on an assist from Colleen Dougherty‘s free kick to tie it up 2-2.
“They scored right after we scored, and that’s the way Oklahoma State is,” Missouri coach Bryan Blitz said. “They’re a conservative, patient team and a counter-attack team.
“We certainly had an opportunity to win the game. If you don’t do that against Oklahoma State, you’re going to pay for it.”
The Tigers had a slim advantage in shots, 12-10. But they dominated with 11 corner-kick chances to 2 for OSU.
“We wanted to slow it down a little bit, but they wouldn’t allow it,” Oklahoma State coach Colin Carmichael said. “They want it to be fast, furious and hectic, and they did a good job of making us play that way. Fortunately at the end we were fortunate to find a way to get a couple of goals. They made it hard, but we won at their tempo.”
Strawser scored the first goal of the game on indirect kick after Mallory Stipetich was called for a foul after her attempt to get a foot on the ball instead strayed near the face of Langdon.
When the Tigers beat the Cowgirls in September it was the only time Oklahoma State allowed three goals this year.
The Cowgirls have made up for it since then. The Cowgirls, winners of seven straight, had shutout their last four opponents and five of the last six before playing Mizzou.
Missouri was outshot 6-5 in the first half, but the Tigers had the early advantage in corner kicks (4-2) and might have had the better opportunities. They missed three tries from in or near the goal box.
On a 28th-minute corner kick from Kari Adam, Brittany Hopkins sailed through the air and got a foot on the ball. But her shot was high and shaved the crossbar before continuing past the goal out of bounds.
In the 39th minute Hopkins sent a header into the goal box where Kendra Collins got a foot on it and helped it along and low. But OSU goalkeeper Adrianna Franch managed to fall on it and smother it.
And with just less than two minutes before the end of the half, Hopkins got off her third shot of the period, and this one was almost unopposed because Franch was caught in front of the play while defending the ball. But Hopkins’ header couldn’t get past the near post and went out of bounds to the outside of the net.