The game was tied 3-3, but Texas A&M won the penalty kicks 5-3 when goalkeeper Jordan Day made a late stop and Mathias punched in the final penalty kick.
Texas A&M fell behind 2-0, but the Aggies scored three goals in span of less than five minutes and looked to have the game in hand until Kastor headed in the last-second goal from almost point-blank range off a pass from Ingrid Vidal.
The Aggies (13-5-2) play Missouri in a semifinal Friday at 8 p.m. The sixth-seeded Tigers (12-7-1) played to a 2-2 tie with Baylor on Wednesday but advanced 4-3 on penalty kicks. Kansas is 11-8-1.
Kansas had the 2-0 lead when Liana Salazar, a freshman from Bogata, Columbia, was slid a pass to the right side of the goal from fellow freshman Jamie Fletcher. Even though she was working into a strong wind gusting at more than 20 mph, Salazar put the ball away and the Jayhawks were looking at the upset with 16 ½ minutes to go.
“Being down 2-0 is the worst in soccer to have,” Mathias said. “But they didn’t see the best of this team in the first half. We have a bunch of fighters.”
But it was less than a minute later when the Aggies finally got on the board on Mathias’ seventh goal of the season on an assist from Allie Bailey to cut it to 2-1.
And just 1:12 after that Annie Kunz tied the game up on her 11th goal of the year. Her goal, which shook the crossbar and bounced down and into the goal, was assisted by Beth West and Nora Skelton.
The Aggies went ahead less than four minutes later when Kelly Monogue, who swept the Big 12 Newcomer of the Year and Offensive Player of the Year awards, scored her 17th goal of the season when Kunz’s pass for Mathias slipped past her and found Monogue with less than 11 minutes remaining.
Monogue earlier had a penalty kick following a hand ball ruling in the penalty box against Kansas at the 53rd minute. Her low, nearly straight-on kick was stopped by Kansas redshirt freshman goalkeeper Kaitlyn Stroud.
Two minutes later Monogue, a freshman from McKinney, Texas, had another opportunity driving up the right-hand side. She launched another low one from about 20 yards that scooted wide left.
“I thought we played very well,” Kansas coach Mark Francis said. “In the second half the wind started picking up and it changed things for them. It made it easier for them. Being up 2-0, you‘d like to think we could have held on. But you have to credit them.”
KU rattled off the first two shots on goal for the game, both quality scoring opportunities from Jayhawks midfielder Whitney Berry. She was easily the most active player on the field, and she finally broke through with a goal from about 15 yards out that gave Kansas a 1-0 lead in the 35th minute. It’s her eighth of the season.
With her back to the goal, Berry took a centering pass from Shelby Williamson and spun quickly around and fired a sharp high shot that Aggies freshman goalkeeper Day was late to reach.
The Aggies defeated Kansas in the regular-season meeting 3-0 last month in Lawrence.
This was the 33rd overtime game in conference tournament history and the fifth time that the first day has seen a pair of games decided in overtime. It’s the only the second time, 2007 being the other, that two games on one day of competition were decided by penalty kicks.