The Cougars (3-3) also got 13 points from Jordan Railey in stopping a three-game losing streak.
"A great win for our program," WSU coach Ken Bone said. "We really needed a win. Not only did we win, but I'm really excited the way we handled things down the stretch."
Terone Johnson had 16 points for Purdue (5-2), which was coming off a 97-87 loss Thursday to No. 5 Oklahoma State in which the Boilermakers rallied from a 24-point deficit to get within four with 3:16 to play.
"At halftime, we talked about playing like we were 10 down instead of 10 up," said Purdue coach Matt Painter, whose team led led 27-17 at the half. "Playing with a chip on our shoulder like we did when we played Oklahoma State. They jumped on us and grabbed the momentum pretty quick."
D.J. Shelton had a pair of 3-pointers to key a 14-2 run to open the second half. The surge put Washington State up 31-29 with 16 minutes left. Lacy's 3-pointer gave the Cougars a 49-44 advantage 13 minutes into the half.
"They started knocking down shots and playing together as a team," Purdue guard Bryson Scott said of the Cougars. "We still could have stopped it, but we didn't do a good job on defense as a team. We forced a lot of shots (on offense) that allowed them to keep that momentum."
The Cougars made just 6 of 27 shots (22.2 percent) in the opening half. They went 19-of-29 (65.5 percent) in the second.
"We didn't put our heads down," Lacy said. "We knew we were getting good shots. We just weren't making them."
Purdue entered the game averaging 86.3 points per contest.
"It was a great defensive effort," Bone said. "That's what I'm most proud of, personally. That's a great team. They have a lot of firepower."
Eastern 82, Seattle U 75
CHENEY -- Tyler Harvey scored a career-high 30 points to lead the Eagles (5-2) over the Redhawks (3-3). EWU opened the game on a 19-8 run, but Seattle U chipped away and got the score to 38-35 at halftime.
Everett 86, Spokane 83
LONGVIEW -- R.J. Magar scored 22 points and Theo VandenEkart added 14 points and eight rebounds as Everett Community College defeated Spokane at the Red Devil Classic. The Trojans advanced to today's semifinals.
Seattle U 84, Coastal Carolina 53
SEATTLE -- The Redhawks (2-4) outscored the Chanticleers (4-2) by 24 points in the second half to win on the opening day of the Delta Dental Thanksgiving Tournament. The Redhawks advance to face Cornell in today's dhampionship.
More Sports Headlines
Seahawks promote RB Smith from practice squad; place CB Simon on IR 3:46 p.m. Down 21, Tennessee rallies to beat No. 19 Georgia 38-31 4:46 p.m. NASCAR Sprint Cup race in Charlotte postponed by rain 4:33 p.m. No. 1 Ohio St. scores 28 straight points in 2nd half, top Maryland 49-28 4:32 p.m. No. 3 Baylor routs Kansas 66-7 to stay unbeaten 4:32 p.m. No. 18 Michigan has 3rd shutout in a row, beats No. 13 Northwestern 38-0 4:32 p.m. Prosise scores 3 TDs, No. 15 Notre Dame beats Navy 41-24 4:32 p.m. Texas upsets No. 10 Oklahoma 24-17 4:32 p.m.
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