But thanks to the flexibility provided by recent off-days, manager John Farrell opted to flip-flop that alignment.
Peavy got the ball Tuesday night, which means he can also pitch the finale of the three-game series against the Tigers on Sunday.
Doubront will pitch Wednesday and then again on May 20 against the Blue Jays.
"We had the off-days to work with," said Farrell. "We just wanted another right-hander lined up against Detroit given the way their lineup stacks up, what they're doing against left-handed starting, and more than anything, just the flexibility of the schedule that gives us a chance to match up a little bit better."