KU's Kelly Fitzgerald doubled to lead off the bottom of the 12th before moving to third on Katie Lynch's one-out single to center. Samantha Derr, who pitched the whole way to earn the win for the Golden Bears, connected with a single to left center to drive in Fitzgerald for the game's only run.
UCSD (42-22) faces an elimination game on Friday morning at 9:30 a.m. PDT against St. Joseph's (34-19). The Tritons must win three straight elimination contests to advance to the championship game.
"We'll bounce [back], I'm confident of that," said UCSD head coach Patti Gerckens. "It's a tough loss. Camille pitched [essentially] two good games in one day today, but we didn't have the offense. We're going to bounce back just like we did the last two weekends."
Gaito (30-11) pitched a career-high 11 and one-third innings and did not give up multiple hits in a single frame until the Bears' last at-bat.
UCSD has been in this position before this postseason, having lost its opening game in both the NCAA West Region II tournament and the West Super Regional. The Tritons responded with four wins and two wins in a row, respectively, to stay alive in the NCAA Tournament.
Derr (30-3), a NFCA All-America First Team selection, retired the first 10 Triton batters and had a no-hitter going until Caitlin Brown's one-out single in the top of the seventh.
KU put runners on second and third in the bottom of the fourth inning, but Gaito fanned Heather Hannum before making a play on a tricky ground ball to throw out Lynch at first to end the inning.
Lynch responded by leading off the bottom half of the seventh with a triple into the right field corner. Gaito retired the next hitter and then got Maria Isgro to play a slow grounder to third. Emily McQuaid fielded the ball, looked Lynch back to the bag, and fired over to first in time to get Isgro.
Lynch took off for home on the throw across the diamond, but Brown gunned Lynch down with a textbook strike to Charly Swanberg, who was blocking Lynch's path to the plate. Swanberg held onto the ball despite the collision with Lynch, extending the game for the Tritons.
Kris Lesovsky, who collected two of the three hits against Derr, connected with a double off the top of the wall in left center to put a runner aboard with one out. However, UCSD was unable to capitalize, as Derr struck out Kirsten Willmon before getting Brown to ground out to short.
"That was the best pitcher we've faced all year and she definitely kept us in check. We had plenty of opportunities to make adjustments and we didn't make any," said Gerckens.
The Tritons' final opportunity came in the top of the 12th when Lesovsky led off with a single to center. Willmon attempted to bunt her over, but Derr forced two foul tips before striking Willmon out. Lesovsky was caught at second on Brown's fielder's choice and Mya Romero popped out with a runner aboard to end the inning.
The loss was UCSD's first-ever in the NCAA Championship. The Tritons went 4-0 in their first appearance last season and now stand at 5-1.
St. Joseph's fell in its first contest yesterday, but advanced via a 5-2 win over Flagler in an elimination game on Thursday.
The UCSD-St. Joe's winner will move on to face No. 2 Central Oklahoma at 2:30 PDT on Friday.