At UFC 107 on December 12, 2009, Sanchez fought and lost to BJ Penn for the UFC Lightweight Championship. Early in the first round, Penn landed a right hand that dropped Sanchez, followed by flurry of punches that almost prompted referee Herb Dean to stop the fight. Although Sanchez was able to recover enough to stay in the bout, he was outclassed in the following four rounds that saw Penn dominate with superior stand up, whilst all 27 takedown attempts made by Sanchez were negated by Penn's superior defense. Early in the fifth round, Penn landed a head kick that caused a large cut to be opened up on the forehead of Sanchez. Herb Dean called the action to a halt for doctor's advice and the fight ended at 2:37 by TKO, marking the first time Sanchez has been stopped in a fight. This also marked only the second fight in UFC history to end in the fifth round. At the post-fight press conference, UFC President Dana White was quoted saying Sanchez was "about as busted up as I've ever seen a guy." Sanchez had his bottom lip completely split open, with his left eye swollen shut and a large cut above his left eyebrow.