BYU, which plays the winner of Oregon-Portland State on Friday at noon, had a chance to win the game in the eighth. WAC Player of the Year Delaney Willard struck out with the bases loaded.
The Cougars (44-13), who won for the 20th time in 21 games, were able to advance despite not receiving any offense from the middle of the order. The top of the order drove in three of four runs, including Tiffany Messerschmidt's two-run single in the second that gave BYU a 3-0 lead.
Mississippi State (33-23) scored three in the fifth off of BYU starter Hannah Howell to tie the game. The Bulldogs opened the seventh with back-to-back singles by Kaili Smith and Heidi Sharpe.
Sam Lenahan, who doubled home two runs in the fifth, then rifled a line drive that was snagged by BYU third baseman Ashlee Brawley. The ensuing throw to second baseman Stacie Toney and first baseman Katie Manuma caught the MSU runners off base.
BYU, which chased Mississippi State starter Lindsey Dunlap after three innings, finally broke through against Kylie Vry, who opened the bottom of the ninth by walking Manuma. Carly Duckworth, who ran for Manuma, stole second, forcing the Bulldogs to walk Krista Hicks.
One batter later, Everett doubled home Duckworth with the game-winner.