Heath Herring
O'Brien made his UFC debut at UFC Fight Night 6 on August 17, 2006, against Kristof Midoux and won via TKO in the second round. O'Brien followed this up with a unanimous decision victory at UFC 65 before facing Heath Herring at UFC Fight Night 8 on January 25, 2007. O'Brien picked up perhaps the biggest victory of his career, defeating the PRIDE veteran via unanimous decision (29–28, 30–27, 30–27).