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.