PITTSBURGH -- Boston Red Sox first baseman Triston Casas left Saturday's 4-2 win over the Pittsburgh Pirates with left rib discomfort.

In his postgame media availability, Red Sox manager Alex Cora expressed concern about the injury, adding that Casas, 24, felt something in the rib area during his first at-bat. He was undergoing tests, Cora said after the Red Sox defeated the Pirates for the second time in as many days.

"He's not doing OK," Cora added.

Third baseman Bobby Dalbec replaced Casas at first base in the bottom of the first inning, and Pablo Reyes took over for Dalbec at third for the short-handed Red Sox.

Boston is already managing several injuries to everyday players. Third baseman Rafael Devers (knee) and outfielder Tyler O'Neill (concussion) did not play in the win but could return Tuesday against the Cleveland Guardians, Cora said before Saturday's game.

Casas, Boston's cleanup hitter, has six home runs and 10 RBIs this season. In his first full season last year, he finished with 24 and 65, playing in 131 games for the Red Sox.

Once the lineup and positions were settled, Kutter Crawford allowed one run in six strong innings as the Red Sox handed the Pirates their fifth straight loss. Crawford (1-0) struck out six and walked three. The 28-year-old right-hander gave up a season-high seven hits after not allowing more than three hits in any of his previous four starts.

Kenley Jansen picked up his fifth save, striking out the side in the ninth, including Michael A. Taylor for the second out on an automatic third strike for not being set. Pirates manager Derek Shelton was tossed after arguing the strike call on Taylor.

Pittsburgh lost for the eighth time in 10 games after opening the season 11-5. Pirates ace Mitch Keller (2-2) look the loss after being tagged for four runs and allowed five hits and four walks in six innings.

The Associated Press contributed to this report.