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.