The 25-year-old Dominican went 1-2 with a 5.34 ERA over 26 appearances this season with Triple-A Durham, striking out 21 in 32 innings. He dominated left-handed hitters, holding them to a .167 batting average in 41 at-bats.
De Los Santos, 6-foot and 165 pounds, didn't start playing baseball until he was 16 years old and was signed by the Rays as a free agent in 2007.
Bobby Nightengale is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.