The red Cougars (13-19) will move on to face Wyoming in a second-round game, while the blue Cougars finish their season at 20-12 knowing exactly why it is over.
"You can't have 29 turnovers," said BYU coach Jeff Judkins. "I don't care who you are. The [men's team] found that out last night, and we found it out today. … Turnovers are a really difficult thing. A lot of players don't understand that."
Washington State came up with 20 steals and turned a lot of those into easy layups, especially in the second half.
"Not a lot of mental toughness on our part, and we gave them too many easy baskets," Judkins said. "When you let a team get back in a game by making easy baskets, they get the momentum and it becomes an uphill battle."
Makenzi Pulsipher led BYU with 23 points to cap a standout career, going 9 of 16 from the field. Cassie Broadhead added 14 points, but only two in the second half.
BYU shot 76 percent (16 of 21) in the first half and took a 41-29 lead at the break.
"The downfall [to a great start] is you get complacent," Pulsipher said. "We came out with less fire in the second half."
And the other Cougars had more.
BYU's Kalani Purcell had nine rebounds in the first half, and finished with nine rebounds.
"It is just sad to lose at home to a team you think you are better than," Judkins said.
Washington State scored on its first eight possessions of the third quarter to get back in the game.
BYU seemingly recovered when Pulsipher and Brenna Chase made back-to-back 3-pointers to push the Cougars' lead to 56-45 with four minutes remaining in the third quarter.
But Purcell's layup was BYU's only basket the rest of the quarter, and WSU trailed by just one heading into the fourth.
Washington State took its first lead of the game, 64-62, with 4:24 remaining in the fourth quarter when Ivana Kmetsova made a rebound basket. The red Cougars scored 26 points off turnovers and 12 second-chance points, using the same formula that Saint Mary's used to oust BYU in the West Coast Conference semifinals.
"They scored 26 points off turnovers," Judkins said. "We take that away, we cut that in half, and we win the game."
• The visiting Cougars force BYU into 29 turnovers to get a come-from-behind win in the Women's NIT first-round game.
• BYU blows a 41-29 halftime lead in its final game of the 2016-17 season.
• Makenzi Pulsipher leads BYU with 23 points in her final game as a Cougar.