Joseph Young had 18 points for the Ducks (18-8, 6-8 Pac-12), who appear to be getting back on track after a midseason slump.
It was the third-straight win for Oregon, which started the season 13-0 before losing eight of its next 10.
Sunday's win took some work, however, as the Ducks had to overcome a 31-24 halftime deficit and the absence of Damyean Dotson, who didn't play after starting 60 straight games.
Dotson, 19, was cited and released early Saturday morning for trying to use a fake I.D. to get into a campus-area bar.
He is averaging 10.7 points and 3.5 rebounds this season but tied his season-high with 17 points against Washington last Wednesday.
Jason Calliste started for the first time this season in Dotson's place and scored 12 points.
But it was Moser who sparked the comeback win. He scored the Ducks' first 11 points coming out of halftime, getting his first basket on a steal and dunk four seconds into the second half, followed by 3-pointers on three straight possessions to put Oregon up 35-34 with 18:09 to play.
Though the Ducks never trailed again, they didn't pull away until late when a dunk by Moser and 13 straight points by Young turned Oregon's four-point lead into a 63-46 advantage.
Moser finished 8 for 13 from the field and made 5 of 7 3-point attempts.
DaVonte Lacy scored 19 to lead the Cougars (9-18, 2-13), and D.J. Shelton had 14 points and 10 rebounds.
Washington State shot 27.3 percent in the second half, making just 6 of 25 attempts from the field. The Cougars were also 6 for 22 from the 3-point line.
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