The 18-year-old Townsend is a former top-ranked junior player who reached the third round at the French Open this year. She got into her first US Open main draw with a wild card.
Williams could potentially play Wimbledon champion Petra Kvitova in the semifinals after the draw was held Thursday. Second-seeded Simona Halep and fourth-seeded Agnieszka Radwanska are in the other half. Halep could meet five-time major champ Maria Sharapova in the quarterfinals.
Wimbledon champ Novak Djokovic and Australian Open champ Stan Wawrinka could meet in one semifinal on the men's side. Second-seeded Roger Federer and fourth-seeded David Ferrer are in the other half. Djokovic could face Andy Murray in the quarterfinals.
Center Court: Serena's Back
Greg Garber and Prim Siripipat discuss Serena Williams' chances of winning her sixth US Open title after winning 12 of 13 matches since her bizarre exit at Wimbledon.
Up Or Down: Women's Field
Greg Garber and Prim Siripipat pick three of the biggest names in women's tennis and decide if they're trending up or down (or flatlining).