Santillan (oblique) did not allow a hit or walk while striking out two over a scoreless inning for Triple-A Louisville on Friday.
Santillan opened his rehab assignment with the Bats, dispatching the side in order on 13 pitches (nine strikes) in the seventh inning. The right-handed reliever has been out since late June and may require more than one outing before rejoining the Reds.