Red Sox right-handed pitcher Richard Fitts was cruising along in his outing, working on a shutout Saturday afternoon when he threw a wild sweeper to Miguel Vargas and immediately motioned to the dugout with his fingers.

As Fitts rubbed what seemed to be his pec muscle on the NESN broadcast, Alex Cora and the trainer went to the mound. He was removed from the game with what the team is calling right shoulder pain.

Once Fitts came out of the game, the wheels quickly came off for the Red Sox.

Zack Kelly was summoned from the bullpen and walked Vargas and struck out Nick Maton but left a fastball over the plate, and Luis Robert Jr. crushed it for a two-run opposite-field homer that tied the game.

Before Fitts left the game with the injury, he was putting together a stellar outing, allowing just three baserunners on one walk and two hits while striking out five over five shutout innings. The young righty had looked solid over his first two starts, including coming off a decent outing against the Blue Jays on Monday night at Fenway Park.

“The gameplan was really good. I took a step up, I think, in preparing for the game and even moving on from the last outing, too,” he said. “I really felt strong and comfortable and confident with every pitch. Even through the last pitch, I felt like I could get anybody out with any pitch.”

If the Red Sox lose Fitts, it’ll be a blow to their pitching depth, even though Lucas Giolito and Brayan Bello are making strides to return off the injured list. Fitts has been putting together a nice little start to his big league career, recording a career 2.39 ERA over his first seven starts dating back to September.

The Sox weren’t able to provide a ton of specifics regarding Fitts’ injury, but Cora is concerned, saying that the righty will fly back to Boston on Sunday and undergo an MRI on Monday.

“Whenever you have to come out of the game and talk about MRIs, you always get concerned,” said Cora. “He really wanted to keep going, and my job is to take care of my players. Hopefully, we stopped at the right time, and he didn’t miss too much time.”

Cora said that Fitts felt a sensation in his shoulder before he threw the sweeper that ultimately went wild and resulted in him coming out of the game.

“Something different that I haven’t felt before,” Fitts said. “I felt like I was in a groove, then wasn’t able to throw my best pitches. I had to call them out there.”

Fitts said the pain is close to his shoulder but will wait for the test results to let him know what exactly is wrong.

“It’s close to the shoulder, but we’re going to figure out exactly what’s going on and kind of go from there. We’ve got a good staff, and we’ll figure out what’s going on.”

The uncertainty around his injury, Fitts, who has been the club’s second-best starter behind Garrett Crochet, could be facing a long absence on the mound.

“Hopefully, nothing’s going on,” Fitts said. “I’ve never missed a start in my professional career, and I take a lot of pride in my health.

“It’s really disappointing for it to happen, especially in the game we were having today. But I feel confident in our staff and our team, too, that we’re going to make the right decisions and find out what’s going on.”

CEDDANNE RAFAELA PROVIDED A SPARK

The game was scoreless over the first five frames until catcher Carlos Narváez singled and later came around to score when Ceddanne Rafaela rocketed an RBI triple in left field. It was Rafaela’s first extra-base hit of the season.

The very next batter, Romy Gonzalez, who was penciled into the leadoff spot to give slumping Jarren Duran the day off, connected for a base hit that scored Rafaela from third to make it a 2-0 Sox lead.

Boston’s bottom lineup produced, and Rafaela, who is trying to get out of a slump, went 2-for-4 with a run and an RBI in the fifth.