Beato was acquired from the Mets on Aug. 14 in a trade for catcher Kelly Shoppach. Beato appeared in seven games with the Mets in July, allowing five runs in 4 1/3 innings with five strikeouts.
The Red Sox used seven relievers over six innings during Saturday's 10-9 loss in 12 innings against the Royals. Boston's bullpen also covered 7 1/3 innings on Thursday, when the Red Sox fell to the Angels, 14-13, in 10 innings.
"We brought up Pedro just to make sure the bullpen was all right," Red Sox manager Bobby Valentine said before Sunday's game against the Royals. "We were going to throw Franklin [Morales] back there just in case and decided that's not the best thing to do. I think we're all right, we have four guys who are able to go and that should be fine."
Valentine said right-hander Andrew Bailey was unavailable on Sunday because he's pitched three straight days. The manager said Vicente Padilla is also unavailable after pitching in four out of the last five contests.
Beato tossed three scoreless innings for the PawSox this week. He struck out all three batters he faced on Friday.
In a corresponding roster move, the Red Sox optioned outfielder Che-Hsuan Lin to Pawtucket. He was recalled on Saturday and was a defensive replacement for Cody Ross in the 10th inning. Ross left Saturday's game as a precautionary measure because he twisted his right knee in the outfield in the seventh inning. Ross was back in the lineup on Sunday, though, batting cleanup and playing right field.