Serving at 5-all in the first set, the No. 1-seeded Federer faced three break points and erased them all. He then broke Istomin's serve and was in control from there.
A fourth-time Olympian, Federer has yet to win an singles medal at the Olympics, although he and Swiss teammate Stanislas Wawrinka did win the doubles at Beijing in 2008. Federer is playing his first tournament since winning a record-equaling seventh Wimbledon title.