BOSTON -- The Red Sox called an audible on Wednesday with regard to September callups, summoning an unexpected second wave that included four more pitchers to supplant the under-performing starting rotation and overworked bullpen.

Lefty Bobby Poyner, who is ranked the club's No. 30 prospect by MLB Pipeline, was recalled from Triple-A Pawtucket. Also promoted to the Majors from the PawSox were righties Colten Brewer, Trevor Kelley and Mike Shawaryn, who is the organization's No. 21 prospect.

The original plan was just for the one wave of callups that happened on Sunday, when six players were added to the roster and David Price was activated from the injured list.

But manager Alex Cora asked president of baseball operations Dave Dombrowski to shift course after Rick Porcello lasted just four-plus innings and allowed six runs in Tuesday's 6-5 loss to the Twins.

Boston's rotation entered Wednesday with a 5.03 ERA, which ranks 20th in the Major Leagues.

The Red Sox have a whopping 21 pitchers on their active roster.

"Obviously it's not perfect, but our starters are not giving us enough," said Cora. "We need matchups, we need arms. We're going to try to maximize Brewer's cutter and Shawaryn's slider and Bobby's fastball up and Kelley's side-arm pitches. We're trying to look for outs.

"That's something we talked about last night when I finished here [with the media]. And Dave called me this morning and [was] kind of like, 'What do you think?' I was kind of like, 'You know where I'm at.' Luckily, I work in an organization that, we're not going to tap out, we're not going to wave the white flag and we're going to keep pushing."

Teams won't be able to be nearly this aggressive with callups next year, when a rule change will allow rosters to be at just 28 players in September rather than 40.

"The rules are the rules," Cora said. "Next year, you can't do that. It's probably not the first time that's ever happened in the game, so I don't feel bad about it."

How, specifically, does Cora think the barrage of pitchers can help him manage the final 24 games?

"It would be a good way to kind of like [handle] a bullpen day, and if a starter goes short, we can still try to keep the game in check using matchups," said Cora. "We'll see. I don't know. It's just kind of the way we feel that we can pull this off."