Williams started for his second season on the defensive line as a sophomore in 2013, at end in 2013 after playing tackle in 2012, and had an All-American showing. Overall while starting 13 games (h e suffered a shoulder injury at Oregon State and missed the California game), he was second on USC with 74 tackles, including a team-high 13.5 for losses (with 6 sacks for minus 38 yards), plus he had 1 fumble recover and 2 forced fumbles. He was among 16 semifinalists for the Bednarik Award. He made the 2013 ESPN.com All-American first team, Lindy's All-American second team, AP All-American third team, CBSSports.com All-American third team, Athlon All-American third team, Phil Steele All-American fourth team and SI.com All-American honorable mention, as well as CollegeFootballNews.com Sophomore All-American first team and CBSSports.com Midseason All-American first team. He made the 2013 All-Pac-12 first team, ESPN.com All-Pac-12 first team, Sporting News All-Pac-12 first team, Athlon All-Pac-12 first team and Phil Steele All-Pac-12 first team. He was named USC's Defensive Lineman of the Year. He was bothered during the year with a shoulder injury.