BOSTON -- Boston Red Sox left-hander James Paxton limped off the field after injuring his right lower leg while making a quick move to cover first on a grounder in the opening inning Sunday against Houston.

The Red Sox announced two innings later that it was a right calf strain.

The 35-year-old Paxton turned quickly and was heading off the mound on Yordan Alvarez's grounder to first baseman Dominic Smith. He looked back at the mound briefly, then went down to one knee and struggled to put weight on the leg when he got up.

Red Sox manager Alex Cora and a trainer came out before Paxton limped to the dugout, with the help of the trainer, and slowly made his way down the steps to the clubhouse. Paxton was replaced by righty Lucas Sims after getting just two outs.

Alvarez was safe on the play, as Smith wasn't able to beat him to the bag.

Paxton made his third start since Boston acquired him in a trade from the Los Angeles Dodgers.