American Andy Roddick upset world number three Roger Federer 7-6 (7/4), 1-6, 6-4 in the third round of the Miami Masters.
Roddick, who is seeded 31st, will play either Argentina's Juan Monaco or Gael Monfils of France in the fourth round.
But there was no such trouble for the defending champion Novak Djokovic, who defeated No. 27 seed Viktor Troicki 6-3, 6-4 in an all-Serb clash.
The world number one Djokovic, who won Miami titles in 2007 and 2011, saved seven of eight break point opportunities as he beat Troicki for the 11th consecutive time.
Djokovic finished with two aces, one double fault and won 73 percent of his first-serve points in the 85 minute match.
"Generally I feel that I have been playing well," Djokovic said. "I did have some ups and downs, especially in today's match, but I'm confident that I can raise the level of my performance in every match."
Djokovic next plays 17th seed Richard Gasquet of France.
Women's top seed Victoria Azarenka survived a scare from 16th seeded Dominika Cibulkova, gutting out a 1-6, 7-6 (9/7), 7-5 victory in the fourth round Monday.
Cibulkova made Azarenka, of Belarus, work to protect her season long match win streak which now stands at 26.
"It felt like she closed her eyes and just went for everything, and me, I couldn't really open my eyes," Azarenka said. "It was like I was blinded.
"But my coach came to the court, kicked me a little bit that I have to at least try to change something. It was like a snowball. I kept rolling . and I didn't really adjust.
"In the end I tried to change something. But it was more about fighting in my heart today."
World No. 1 Azarenka struggled in the first set then needed a tiebreaker in the second to get back into the marathon two hour, 47 minute match. She finished with two aces and seven double faults, compared to Czech Cibulkova's 10 double faults.
Azarenka advances to face France's Marion Bartoli, who easily defeated Maria Kirilenko 6-1, 6-2 earlier in the day.
World No. 2 Maria Sharapova defeated fellow Russian Ekaterina Makarova 6-4, 7-6 (7/3) to set up a quarter-final clash with China's Li Na.
Sharapova, the 2011 Miami runner-up, is chasing her first title at the event after finishing second three times. She lost in the final last year to Azarenka.
"I felt like I was up a set and a break, and played a bit sloppy," Sharapova said. "Combination of her stepping up, and being much more aggressive. She had opportunities, served for the second set.
"I just hung in there and stayed consistent. I played a much smarter tiebreaker, and I think that helped me."
Sharapova saved break point 11 of 15 times and converted on five of eight of her break point opportunities to advance into a matchup against Li, who rallied to beat Sabine Lisicki 3-6, 6-4, 6-2.
Sharapova double faulted 11 times but shrugged it off.
"Yeah, it's definitely not easy to play with that," Sharapova said. "But I managed to win the match in two sets, so that's a plus.
"Definitely consistency will be really important in the next match and getting the percentage up, and also returning a little bit better, little things here and there."
American 10th seed Serena Williams defeated Australian sixth seed Samantha Stosur 7-5, 6-3 in a rematch of the 2011 US Open final.