Several hours before first pitch on Sunday, several Red Sox players and coaches took the field to run through some pregame ground ball drills. Two of those were rookies Marcelo Mayer and Kristian Campbell, and the sight of the top prospects working together at Fenway Park was one fans have long dreamed of.

The only thing was, most people probably envisioned Campbell and Mayer working together at second base and shortstop, not first and third base.

With the Red Sox ravaged by injury, two of the club’s “Big Three” have now reached the majors but will likely spend a good amount of time playing unfamiliar positions out of necessity.

Mayer is primarily a shortstop who has lately spent more time at second base in anticipation of his potential call-up, but following Alex Bregman’s injury the 22-year-old is expected to get most of his time at third base, where he’d only ever played six games professionally in the minors prior to his MLB debut on Saturday.

Campbell, meanwhile, remains Boston’s everyday second baseman but is being groomed for a potential move to first base to help fill the void left by the injuries to Triston Casas and Romy Gonzalez.

However the opportunities may come it’s still an exciting time for the Red Sox, who finally get to see some of their most acclaimed young players compete on the highest stage.

Though as Campbell’s last few weeks have shown, there will be growing pains along the way.

Mayer’s MLB debut on Saturday was a whirlwind, and while the day nearly had a storybook ending with Mayer coming up in a huge spot in the ninth inning, the rookie still finished 0 for 4 with three strikeouts in his first game. Cora said that for all Mayer’s poise he was still understandably nervous, but going forward he expects Mayer will settle in as things get back to normal.

“One thing I told him was enjoy it, it doesn’t matter the result. 0 for 4 with four strikeouts or 4 for 4 with four home runs, whatever, just enjoy it, you’re a big leaguer and no one is going to take that away from you,” Cora said. “Now I think his family flew in, they made it, so he’s playing. He’s going to have a blast anyway, he loves the game, we met today to go over a few things and he’s excited about the opportunity. But yesterday was fast. Very, very fast.”

Mayer was back in the lineup again Sunday batting sixth, right behind Campbell in the five spot. It might look a little different now, but if things go according to plan Red Sox fans can expect to see those two together in the middle of the order for a long time.

Starters announced

Cora announced the club’s starters for the upcoming series against the Milwaukee Brewers, saying Garrett Crochet will pitch the opener on Monday, Tuesday’s starter remains to be determined, and Brayan Bello will pitch the finale on Wednesday.

None of Boston’s five starters are expected to be available on regular rest Tuesday as a result of this past week’s postponements and Saturday’s doubleheader. The Red Sox will most likely instead need to call up a spot starter or attempt a bullpen game.

Extra innings

While Alex Bregman (right quad strain) is highly regarded for his impact in the clubhouse, Cora said the third baseman won’t travel with the team on road trips while he’s on the IL so that he can focus on his rehab. … Richard Fitts (right pectoral strain) is expected to make his next rehab start on Tuesday when the WooSox travel to Scranton/Wilkes-Barre. … Infielder Romy Gonzalez (left quad contusion) will most likely need to go on a rehab assignment before he’s ready to return to the majors, Cora said.