Shimmick, a freshman forward from Grapevine, Texas, added her second goal in the 80th minute to complete the scoring after UT went up 2-0 after 30 minutes. The goals were her second and third of the season.
"I knew I had it in me," Shimmick said. "I was feeling really good. I was joking in warmups, 'I'm on fire today. We got this.' We knew if we kept on pressuring them and if we kept on going they would get tired and eventually the holes would open up."
Texas (8-10-1) snapped a three-match losing streak and advanced past the first-round of the conference tournament for the second consecutive year. It took a top-seeded team to eliminate the Longhorns last year (Oklahoma State), and UT might face that situation again in Friday's semifinals. The Longhorns will face the winner of the No. 1-seed West Virginia-TCU match to be played later Wednesday.
UT lost to West Virginia 1-0 in overtime last week to finish the regular season.
The Longhorns spent plenty of time in OU's end of the field in the first half, yet found a way to keep OU from mounting much offensively through the entire game. The Sooners (7-9-4) got off five shots the entire match, less than half of their average of 12 per game during the regular season.
"The best form of defense can often be your offense," Texas coach Angela Kelly said.
Two of those shots by OU made it back to Texas goalkeeper Abby Smith, the freshman second-team All-Big 12 selection who rather easily was credited for her sixth shutout of the season.
"The disappointing thing was that (Texas) was the aggressor and we didn't come to play," OU coach Matt Potter said. "It's a do-or-doe thing, you have one opportunity. By the time we started to collect ourselves they had gotten ahead and they played a different way."
Within the first seven minutes, UT got two close-in looks before OU showed some life with a response in transition. OU goalkeeper Kelsey Devonshire was quickly forced to get a hand in there to knock away a centering pass that made it to the foot of Longhorns forward Hannah Higgins, and less than a minute later Devonshire had to reach and deflect a shot by Brooke Gilbert.
With all the flurry around the Sooners net, OU was handed an opportunity. It came following a shot from UT's Chantalle Campbell, which Sooners defender Katharine Nutman blocked. The rebound caromed downfield and set up a 2-on-2 break that OU almost converted when Samantha Howell's breakaway shot from inside 20 yards was turned away by Smith in the 13th minute.
It wasn't long before another couple of pushes up field by the Longhorns ended with the ball in the back of the net.
Near the end of the 23rd minute Campbell sent a pass to her left for Shimmick to advance. Nearing the end line, Shimmick turned it back and passed to Kristin Cummins, who was joined by OU defender Emily Bowman. The ball rose up between Cummins and Bowman, but it was ruled an own goal when it appeared to bounce off Bowman and bounded by Devonshire.
"Whatever goes in the box has a chance of going in," Shimmick said.
Campbell was active again four minutes later, her centering pass redirected from 14 yards out by Shimmick for goal No. 2.
By that time UT had taken five of the match's first seven shots and managed to get four of them on goal.
OU's best answer came in the 38th minute when Annalisa Hall sent a liner in from past the left side of the box that Smith had to backpeddle to deflect.