Five-times Wimbledon winner Williams faces Serbia's Jelena Jankovic in the second match on the 15,000 capacity court and is followed by Federer, who lifted the trophy for the seventh time this month, against Colombia's Alejandro Falla.
In the opening match at midday, sixth-seeded Czech Tomas Berdych will play Belgium's Steve Darcis.
"It is one of the biggest (matches of my career)," Darcis told reporters at a Belgian tennis team press conference at Wimbledon on Friday.
"It's the first time I have played on Centre Court so it will be a little bit strange at the beginning, but it's the Olympics and a totally different atmosphere. Of course, it's a very tough match, a very tough opponent so you never know what can happen. I will do my best and we will see how it goes."
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.