The Ducks started the game shooting a blistering 12 of 16 from the floor and led 31-12 after a Jason Calliste three-pointer at the 10:39 mark. Oregon went seven for seven on three-pointers during the stretch, with Moser making three.
"For a while there, we were 100 percent. You just didn't want to be that guy to miss," said Moser, who finished with 15 points and seven rebounds.
"Taking good shots, good shooters were shooting the ball, good passes. Just knocking it down," said Ducks point guard Johnathan Loyd.
Joseph Young scored 25 points for Oregon (16-8, 4-8 Pac-12), which had five players in double figures.
Eric Moreland led Oregon State with 17 points and 10 rebounds, while Roberto Nelson scored 18 for the Beavers (13-11, 5-7 Pac-12), who have lost three in a row.
"You can't play any game, let alone the Civil War game, where you start the game off and give them a 19-point lead," said Oregon State Coach Craig Robinson.
After falling behind early, Oregon State responded with a 15-3 run, making it 34-27 after a Nelson breakaway lay-in with 5:13 left in the half.
But the Ducks pulled away again and took a 45-35 advantage into the break.
In the second half, the Beavers twice trimmed the lead to two points, the latter when Hallice Cooke sank two free throws to make the score 72-70 with 5:11 remaining.
Missed shots and offensive fouls on two straight possessions doomed any hope of a comeback for the Beavers, and the Ducks went on a 9-0 run capped by another Calliste three-pointer with 2:51 left.
Oregon made 12 of 14 free throws in the final two minutes to seal the victory.
The Ducks were 11 of 21 on three-pointers. Ironically, long-range shooting has been a strength for the Beavers this season.
Oregon State entered the game ranked first in the Pac-12 and fifth in the nation for 3-point shooting at 41.4 percent. That figure would be a school record if it holds for the rest of the year.
The Beavers, who entered the game fifth in the nation by making 41.4% from long range, finished five of 16 from beyond the arc.