Boise pitcher Julian Fernandez walked in the winning run in the bottom of the 10th inning as the Hawks lost 3-2 late Friday night.
Fernandez walked three batters and gave up one hit in one-third of an inning to take his second loss of the season.
Everett took the early lead with a run in the first inning. Both team scored in the sixth, and Boise tied it up 2-2 on a Jacob Bosiokovic home run in the top of the seventh.
Despite the close score, Everett outhit Boise 8-3.
The Hawks (2-6) continue their five-game Northwest League series against the AquaSox on Saturday.