Garrity made three 3-pointers and added six assists for the Hornets (11-10, 6-7 Big Sky), who came in with three one-point losses in conference play, including Monday's 62-61 heartbreaker to Northern Arizona.
Collin Chiverton had 12 points off the bench for the Eagles (6-17, 4-9).
Sacramento State led for most of the game, but Eastern Washington pulled ahead midway through the second half and led 48-44 after Thomas Reuter's 3-pointer with 8:43 to play. Sacramento State scored the next 10 points, capped by Mikh McKinney's two free throws with 4:15 left, to take the lead for good.
The Hornets led by as many as eight points in the first half before the Eagles closed the gap to 29-27 at halftime.
Former Kentucky guard Ed Davender, the only Wildcat with at least 1,500 points and 400 assists, has died. He was 49.
Guard Naz Mitrou-Long, whose 2015-16 season ended in December due to hip problems, has been granted a hardship waiver for the coming season, Iowa State said.
As the Sooners look to life without superstar Buddy Hield and his sidekicks, it's clear their unseasoned players will need to grow up fast.