Runzler, a ninth-round selection for the Giants in the 2007 First-Year Player Draft, had his best season in 2009, when he rose through every Minor League classification. He then pitched in 11 games for the big league club that September, allowing just one run in 8 2/3 innings.
He struggled from then on, however, posting a 5.68 ERA and a 1.82 WHIP this season with Triple-A Fresno.
"He did lose some command, which happens," manager Bruce Bochy said. "Sometimes it can be a mental issue, more so than physical. I think that's more the case with Runz. He's got great stuff, and you never know -- something could click there, where he gets back to being the pitcher he was when we called him up."
Tanaka, meanwhile, played in 15 games this season with the big league club and had eight singles in 30 at-bats. The 32-year-old, who had transitioned from second base to left field, hit .329 with Fresno this season. He had previously spent 13 seasons in the Japanese League with the Nippon Ham Fighters.
AJ Cassavell is a reporter for MLB.com. Follow him on Twitter @ajcassavell. This story was not subject to the approval of Major League Baseball or its clubs.