Shortstop Khalil Greene was activated from the 15-day disabled list and started against the Diamondbacks.
Greene had been out since breaking his left big toe while diving for a ball against Philadelphia on Aug. 14.
Greene is batting .257 with 10 home runs and 49 RBI in 92 games.
"Anytime you get one of your core players back, it's a spark to your team," manager Bruce Bochy said.
To make room on the roster, shortstop Wilson Valdez was designated for assignment.
Padres Activate Khalil Greene