Williams saw five carries for 21 yards during Sunday's win over the 49ers.
The rookie got some work in with the Bills being way ahead in the fourth quarter. While Shady McCoy stole the show, it does appear Williams has worked his way into the No. 3 role, with Mike Gillislee firmly implanted as the No. 2. Reggie Bush, meanwhile, has just six rushing attempts for five yards all season.