The host Sacramento River Cats scored two runs in the eighth inning and then held off Tucson in a 5-3 win Friday night.
The Padres (66-61) trail division leaders Las Vegas and Sacramento by four games.
The Padres fell behind 3-0 on single runs in the first three innings.
Tucson began chipping away at the deficit when Brandon Allen led off the fourth with a triple and scored on Ben Francisco's sacrifice fly.
Allen had an RBI single to right in the sixth to pull Tucson within one.
But Michael Taylor's sacrifice fly and Ryan Ortiz's line-drive RBI single to right off Miles Mikolas gave the River Cats a three-run cushion in the eighth.
Scott Moore smacked a lead-off home run in the ninth to cut the deficit to 5-3, but Brian Gordon closed out the win for the River Cats with three strikeouts.
Tucson starter Anthony Bass (3-6) gave up eight hits and three runs over five innings.
Compiled from a news release