"He did a good job for us," Giants manager Bruce Bochy said of Pena, 31. "But we had to make room."
Judged to be sufficiently recovered from a right hamstring injury and subsequent surgery, Pence appeared in his first Major League game since June 1. The Giants posted a 26-22 record in his absence.
Crawford, Span day to day
Giants shortstop Brandon Crawford (bruised left thumb) and center fielder Denard Span (sore quadriceps) were out of Saturday's starting lineup as they nursed their respective injuries, which they sustained Friday. Giants manager Bruce Bochy rated their playing status as day to day.
"I'd say that it's more doubtful for Span," said Bochy.
Span bunted into a fielder's choice as a pinch-hitter Saturday, but was replaced by pinch-runner Jeff Samardzija after limping to first.
Crawford, who was inserted for defensive help in Saturday's ninth inning, said he got jammed by a pitch in his second at-bat Friday. Span was hurt when he collided with Nationals first baseman Clint Robinson while legging out an eighth-inning bunt single.
Crawford, the National League's reigning Gold Glove and Silver Slugger winner at his position, didn't rule out playing Sunday.
"Sometimes these things get better in a day or two. Sometimes they linger," he said.
Chris Haft has covered the Giants since 2005, and for MLB.com since 2007. Follow him on Twitter at @sfgiantsbeat and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.