Zito, who's pitched to a 5.09 ERA across 21 starts this season, coughed up four runs in just 3 1/3 innings against the Phillies on Tuesday, which prompted manager Bruce Bochy to make the move.
"How long this is going to be, I can't tell you, but it was time to change it up so (Zito) will be in long relief," Bochy told the AP. "Sometimes it's just time for a change. You get in a rut."
Guillermo Moscoso will take Zito's next scheduled start on Sunday against the Rays. As well, right-hander Ryan Vogelsong is slated to return from a minor-league rehab assignment late next week, barring setback.
Worth noting: Zito, 35, needs 104 1/3 more innings this season in order for his $18-million option for 2014 to vest. However, that wasn't going to happen even if he remained in the rotation.