Washington State (8-5, 1-0 Pac-12) closed the game on a 12-3 run thanks to Flynn and Josh Hawkinson. Trailing 71-67, Flynn and Hawkinson took over, combining to score the final 12 points for the Cougars and give them their first conference victory in nearly a calendar year.
Hawkinson finished with 26 points and eight rebounds, while Flynn made 6 of 10 shots and added six assists.
Markelle Fultz led Washington (7-6, 0-1) with 26 points, 11 assists and nine rebounds, falling just short of the first triple-double in Washington history. But after carrying Washington for most of the second half, Fultz went scoreless in the final 2 1/2 minutes.
Noah Dickerson added 19 points for the Huskies.
Washington led by as many as 13 in the first half, only to see Washington State surge in the opening moments of the second half. The Cougars scored the first 14 points of the half and built a 49-41 lead before David Crisp finally knocked down the Huskies first shot of the half.
Washington's rally was on the shoulders of Fultz. He spent the first 25 minutes getting others involved, before taking over to rally the Huskies. Fultz scored nine of 13 points during a 5 1/2 minute stretch to pull Washington even at 64-64 with 7:37 remaining after a layup by Dickerson.
Washington State briefly took a 67-66 lead after Hawkinson split a pair of free throws with 4:20 remaining, but Fultz's 17-footer with 3:22 remaining put the Huskies ahead 68-67. Less than a minute later, Fultz's 3-pointer over Hawkinson as the shot clock expired extended the lead to 71-67.
Flynn answered quickly with a driving layup and Hawkinson's basket underneath with 1:36 left pulled the Cougars even at 71-71.
Fultz turned the ball over on Washington's next possession and Flynn beat Crisp off a screen and scored with 48.6 remaining to give Washington State the lead. Fultz missed a driving layup with his left hand and rather than foul, Washington played out the remaining time. Flynn beat Dickerson off the dribble and scored at the rim with 13.9 seconds left for a four-point lead.
Washington State: The Cougars snapped an eight-game losing streak in conference openers. Washington State's last conference opening victory came in the 2007-08 season when the Cougars beat Washington 56-52 in Seattle.
Washington: Fultz got little help from his supporting cast outside of Dickerson. Washington's other three starters -- Crisp, Matisse Thybulle and Malik Dime -- combined for just 18 points.
Washington State: The Cougars face Oregon State in Spokane on Wednesday.
Washington: The Huskies host No. 21 Oregon on Wednesday.