The Miami Open has lost its share of stars in the early rounds of the men's singles tournament, as four of the world's top five men's tennis players have fallen to upsets or retired from the tournament, including second-ranked Andy Murray's upset loss to Grigor Dimitrov in the round of 32.

While the Miami Open has lost four of the world's top five men's tennis players, top-ranked Novak Djokovic remains, as he took down 14th-ranked Dominic Thiem in straight sets on Tuesday 6-3, 6-4. The 22-year-old Austrian pushed the world's number one men's tennis player but was unable to capitalize in crucial moments of the two-hour match.

"I stayed tough when it was most needed. In the most important moments I just tried to make him play, make him run," said Djokovic following the match. "He has very powerful strokes from the back of the court, so he either makes some really amazing shots, down the line mostly, and some great inside out forehands, or he makes a mistake. It was a straight-set win, but far from easy."

Djokovic is now 25-1 on the year and is looking to become the first three-time consecutive champion at the Miami Open since Andre Agassi did it in 2001, 2002 and 2003. The Serbian star now faces seventh-ranked Tomas Berdych in the quarterfinals of the Miami Open.

Berdych is coming off a strong win over 10th-ranked Richard Gasquet 6-4, 3-6, 7-5. It's the seventh time Berdych has reached the quarterfinals at the Miami Open, and he's looking for his first win over Djokovic since 2013 in Italy. Djokovic holds a 22-2 record over seventh-ranked Berdych but knows not to take any opponent lightly, as the Miami Open has shown plenty of examples of higher seeds being knocked out in upsets.

"I'm just going to try and focus on my game, try to play some good tennis, stick with the things that are working well so far for me and just try to go for it no matter who's going to be the opponent," said Berdych.

While the Miami Open has lost multiple of the world's top tennis stars, the quarterfinals has some intriguing matchups, with 15th-ranked David Goffin facing 19th ranked Gilles Simon, 12th-ranked Milos Raonic playing 26th-ranked Nick Kyrgios, and sixth-ranked Kei Nishikori facing 16th-ranked Gael Monfils.

Djokovic should still be considered the favorite based on his continued phenomenal play this year, but don't count out the possibility of an upset, as the Miami Open has had no shortage of upsets in this year's tournament.