Williams, Federer in action on first day

Swiss tennis player Roger Federer answers a reporter's question during a news conference in the Olympic media centre before the start of the London 2012 Olympic Games July 26, 2012.

LONDON (Reuters) - Wimbledon champions Serena Williams and Roger Federer are in action on the opening day of the Olympic tennis tournament on Saturday, returning to the center court just three weeks after their triumphs.

Williams faces Serbia's Jelena Jankovic in the second match on the 15,000 capacity court and is followed by Federer against Colombia's Alejandro Falla.

In the opening match, sixth seed Czech Tomas Berdych will play Belgium's Steve Darcis.

Federer's doubles partner Stanislas Wawrinka, and fellow flag bearers including Serbia's Novak Djokovic, Russia's Maria Sharapova and Wimbledon runner-up Poland's Agnieszka Radwanska have avoided an early start after Friday's late night opening ceremony, all beginning their first round matches on Sunday.

In the doubles, number one seeds American brothers Mike and Bob Bryan will play Brazil's Thomaz Bellucci and Andre Sa on Court 14. (Reporting by Kylie MacLellan, Editing by Nigel Hunt)