It happened just after midnight inside the Savemart store on Clinton and Blackstone.
Fresno police say two men armed with a gun confronted two store employees after the store closed for the night.
They hit one of the employees in the head, and tied up a third employee who they left in a refrigerated area of the store.
At some point two of the workers managed to escape and flag down a patrol car in the area.
But the suspects got away.
"We don't know how they got inside the store, either hid after the store closed. We're trying to determine that," Lt. Tom Rowe said.
Investigators are now reviewing surveillance video to try to identify the suspects.
