Jo-Wilfried Tsonga beat Milos Raonic in the longest tennis match in Olympic history to reach the third round.
The Frenchman won 6-3 3-6 25-23 after three hours and 56 minutes, following a third and final set lasting 48 games - itself an Olympic record.
Tsonga wasted three match points before winning the epic deciding set.
The 66-game contest also beat the previous record of 48 games, set in 2004 when Fernando Gonzalez beat Taylor Dent to win bronze in Athens.
Chile's Gonzalez eventually won that match 6-4 2-6 16-14 after a then-record three hours 25 minutes.
thrashed Andy Roddick of the United States 6-2 6-1 to reach round three.
The second seed, a bronze medallist in Beijing, took only 54 minutes to overcome Roddick and will now play Australian
who beat 13th seed Marin Cilic 6-4 7-5.
World number two Djokovic, who was beaten in the 2012 Wimbledon semi-finals by Roger Federer, said he was enjoying the different atmosphere of the Olympics.
"You're not playing for yourself like you are most of the time throughout the year," said the 25-year-old.
"This is one of the unique events, unique opportunities to play for your country, and the nation is cheering for you as an athlete, as a representative of the nation at this Olympic Games.
"I served extremely well during these opening two matches and [against Roddick] everything was working perfectly well.
"I was neutralising his serve by getting a lot of returns back in the court and serving a lot of aces. Getting a lot of free points on serve is something I really want to have in my game."
moved closer to a fourth Olympic gold as she reached the third round with a 6-1 6-3 win over Aleksandra Wozniak of Canada.