"We just wanted to break up the left-handers and the way it was falling, we wanted to give Rodriguez a couple of extra days," Red Sox manager John Farrell said. "That was the alignment that fit best."
Miley finished the first half 8-8 with a 4.80 ERA. In his last start on Sunday against the Yankees, he allowed six runs on seven hits in 5 1/3 innings for the loss.
Porcello had a rough first half, going 5-9 with an American League-worst 5.90 ERA. However, he ended it on a positive note, allowing two runs on eight hits in six innings against the Marlins for the win.
Rodriguez has been a bright spot in the Red Sox rotation. Called up at the end of May, the left-hander went 5-2 with a 3.59 ERA in nine starts. In his last outing before the break, Rodriguez allowed two runs on five hits in 6 1/3 innings against the Yankees to earn the win.
Boston has yet to announce who will start the series finale on Monday. However, Farrell did say that Brian Johnson will start either Monday or Tuesday's series opener against the Astros in Houston.
Johnson, Boston's No. 6 prospect according to MLB.com, was called up on Saturday to replace Clay Buchholz, who was placed on the disabled list with a strained right flexor.
Farrell said Buchholz's symptoms continue to subside, but the right-hander has yet to pick up a ball.
"He's in the midst of the initial shutdown period. No definitive number of days in which a ball will be put back in his hands," Farrell said. "He continues to improve daily."
Justin Masterson, meanwhile, is expected to pitch out of the bullpen for the foreseeable future.
"We have a need to add to the right-handed group that we have relied heavily on. We are looking to get him in that mix," Farrell said. "It will be dependent upon his performance and the higher leverage that might come with that if we get him on a roll. We just feel like matching him up against some right-handers could be beneficial in shorter stints."
• Right-hander Matt Barnes was optioned to Triple-A Pawtucket on Sunday. The corresponding move will come on Friday, with either Dustin Pedroiabeing activated from the disabled list or the team calling up a reliever.
Quinn Roberts is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.