Townsend is a former top-ranked junior player who reached the third round at the French Open this year. She got into her first U.S. Open main draw with a wild card.
On the men's side, Wimbledon champ Novak Djokovic and Australian Open champ Stan Wawrinka could meet in one semifinal. Second-seeded Roger Federer and fourth-seeded David Ferrer are in the other half.
Djokovic could face Andy Murray in the quarterfinals. Murray beat Djokovic for both his major titles but has struggled some this year after back surgery and is seeded eighth.
Wawrinka could meet Wimbledon semifinalist Milos Raonic in the quarterfinals. The seventh-seeded Gregor Dimitrov, the other young player to break through with a semifinal run at Wimbledon, could face Federer in the quarters.
Howard on 1-year break from U.S. team
SOCCER • Star goalkeeper Tim Howard is taking a one-year break from U.S. national team duties.
The three-time World Cup veteran has asked U.S. coach Jurgen Klinsmann not to consider him for selection to the roster until September 2015. The decision is driven mainly by his desire to spend more time with his family.
Howard, 35, will continue playing for Everton in the English Premier League.
Leg injury may cost Moelgg ski season
SKIING • Italian skier Manfred Moelgg could miss the entire Alpine skiing season because of serious right leg injury.
The Italian ski federation says the 32-year-old Moelgg had surgery after rupturing his right Achilles tendon in training.
The federation says he intends to return to competitive racing.
Moelgg won bronze in the giant slalom at the 2013 world championships, a race won by Ted Ligety of the United States. Ligety is favored to retain his world title in February in Colorado.
Moelgg has also won silver and bronze medals in slalom at the worlds, and was the World Cup slalom champion in 2008.
From wire reports