Nellum won the 400 on Friday, earning 10 points that increased the Trojans' total to 32 and moved them into a first-place tie with Texas.
Arkansas is right behind with 30.5 entering the final day of competition.
Nellum and USC's Aaron Brown are in the 200 final.
Nellum qualified with a time of 19.99 seconds, Brown 20.56.
The USC women's 4x100 relay team of Loudia Laarman, Jenna Puterbaugh, Jessica Davis and Vanessa Jones also will compete Saturday.