Roger Federer's 16-match winning streak came to an end when he was beaten 7-6 (7-4) 1-6 6-4 by Andy Roddick in the third round of the Miami Masters.
"I came out flat today," the Swiss said. "I was a bit tired, I guess."
World number one
secured his place in round four with a 6-3 6-4 win over fellow Serbian Victor Troicki.
In the women's draw, top seed
progressed to the quarter-final stage by beating Slovakian Dominika Cibulkova 1-6 7-6 (9-7) 7-5.
Having lost the second set, Roddick survived three break points in the opening game of the decider and then broke Federer immediately.
It was only the American's third victory in 24 meetings against Federer and ended a losing sequence against top-three players stretching back to 2010.
"That's maybe 30 matches for the season. I am just feeling like it's taken its toll a bit," said Federer, who has won tournaments in Rotterdam, Dubai and Indian Wells this year.
Djokovic needed only 85 minutes to secure victory but had to save seven break points on his way to the last 16.
The Serbian will meet
for a place in the quarter-finals after the Frenchman's win over Albert Ramos.
beat Brit Heather Watson in the previous round,
edged a marathon match lasting two hours and 49 minutes.
The Belarusian's winning run, which now stretches to 26 games, looked in serious jeopardy after she lost the first set.
"I definitely wasn't thinking about the streak, that's for sure," Azarenka said.
"It felt like she closed her eyes and just went for everything and I couldn't really just open my eyes. I was just blinded a little."
Former world number one
- five-time winner of this tournament - beat sixth seed Sam Stosur 7-5 6-3 to set up a quarter-final encounter with fourth seed
who saw off Yanina Wickmayer 7-6 (8-6) 6-0.
6-4 7-6 (7-3) victory over Ekaterina Makarova secured a last-eight clash with
, a 3-6 6-4 6-2 winner over Sabine Lasicki.
needed only 66 minutes to dispatch Maria Kirilenko 6-1 6-2.