Santillan is committed to play college baseball for Texas Tech should he not turn professional.
A couple of hours earlier on Monday evening, the Reds used their first-round selection (No. 11 overall) on catcher Tyler Stephenson from Kennesaw Mountain High School in Georgia.
The Draft continues on Tuesday. The MLB.com preview show begins at 12:30 p.m. ET, with exclusive coverage of Rounds 3-10 beginning at 1 p.m. ET.
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, follow him on Twitter @m_sheldon and Facebook and listen to his podcast.