TUCSON, Ariz. -- Arizona coach Sean Miller moved Kevin Parrom into the starting lineup three games ago, and the senior wing made that move look smart Saturday.
Parrom scored a season-high 19 points, making five 3-pointers, as the 12th-ranked Wildcats held off a second-half challenge from Washington State, 73-56, at McKale Center.
Miller, steamed about his team's lack of effort on defense after halftime, said Parrom saved the day with his shooting and team-high seven rebounds.
"A senior, late in February, has a lot at stake," Miller said. "I don't know where we would be in this game if Kevin didn't play the way he played."
Parrom, who was scoreless in a victory over Washington on Wednesday, hit three 3-pointers in a 72-second span of the second half after the Cougars had trimmed the lead to 49-38.
When Parrom hit the last shot in his flurry, Arizona led, 58-42, with 5:55 to go and then eased in for the victory against the last-place team in the Pac-12.
"I was patient," Parrom said. "I think these last couple of games I've been trying to hunt for my shot rather than let it come to me. My teammates helped me out by getting me open shots."
Point guard Mark Lyons added 14 points for Arizona (23-4, 11-4 in the Pac-12), which entered Saturday tied with Oregon for the conference lead. The Ducks played at Stanford on Saturday night.
Washington State (11-17, 2-13) has lost eight consecutive games, its longest streak since losing 13 in a row during the 2002-03 season. Senior post Brock Motum led Washington State with 20 points and sophomore guard DaVonte Lacy added 10.
Motum hit 7-of-13 shots and got to the line 11 times.
"I need to attack more at the perimeter," Motum said. "I lost my way a bit, but I think tonight I found my way back to what I was doing at the beginning of the season.
"I need to get to the free throw line more, hopefully make more free throws, and keep attacking."
The Cougars didn't help themselves at the free-throw line, making only 14-of-28.
"We've shot a lot of free throws the last few days," Washington State coach Ken Bone said. "I think if you don't work on it, you deserve to do poorly, but we do.
"It's just that some days you make them and some days you don't."
Parrom's offense and the final margin of victory didn't hide the disappointment Miller had in his team's defense.
Arizona, after a strong defensive first half, allowed Washington State to make 52.2 percent of its shots in the second half. The Cougars also shot 22 free throws after halftime.
"It's terrible; it's not going to work," Miller said of his defense, also porous after halftime in recent losses to Cal and Colorado.
"We have worked really hard, practiced 80 times, and I'm proud of a lot of things, but right now, that's not going to work. Guys gotta try. We pick and choose how hard we play on defense.
"It's all effort. One hundred percent. Caring. Playing as hard as you possibly can. Running as fast as you possibly can. Trying not to get screened. Talking. Taking charges. Staying down around the basket."
Parrom, who was making his third consecutive start after starting only one of the first 24 games, eclipsed his previous season high of 17 points, set against San Diego State on Dec. 25.
Against Washington State, Parrom made 6-of-7 shots, including 5-of-6 from 3-point range.
Arizona freshman center Kaleb Tarczewski, who had scored 10 points in five games, set a career-high with 12.
Arizona trailed only at 2-0 and quickly took control as Parrom hit two 3-pointers within the first 81 seconds.
The Wildcats' defense was in command early, holding Washington State without a field goal for exactly 10 minutes, ending when D.J. Shelton hit a jumper with 8:20 left in the half.