The U.S. Open, one of the biggest tennis tournaments in the world, began last week in Flushing Meadows. There have already been plenty of surprising outcomes in these few short days. The most surprising is the downfall of the great Roger Federer of Switzerland. Federer lost in straight sets to Tommy Robredo of Spain in the fourth round this weekend. 

The first set was a close one, resulting in a tie breaker which Federer lost 3-7.  He continued to falter in the second and third set with a total score for the whole match of 6-7 (3-7), 3-6, and 4-6. 

Following the match, Federer admitted that the reason for his loss was his own fault. By the end of the match, he had accumulated 43 unforced errors and could not seem to win the most critical points of the match. 

Robredo, however, played extremely well against Federer and was humbled by the experience, giving homage to him, "For me, Roger for the moment is the best player of all times." 

Robredo will go on to play in the quarterfinals against Rafael Nadal, who won his match yesterday against Philipp Kohlschreiber, 6-7 (4-7), 6-4, 6-3, 6-1. Although Nadal lost the first set in a tie breaker, he was able to focus and pull through during the next three sets. Nadal is looking stronger than ever and is always a crowd favorite to watch.

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Also advancing to the men's quarterfinals are Frenchman Richard Gasquet and David Ferrer of Spain while others are currently battling it out for the last remaining spots. Those amongst them are top-ranked Novak Djokavic, recent Wimbledon winner Andy Murray and Lleyton Hewitt, who is made a short comeback after staying in the background for some time. Hewitt fell short in a promising match against Mikhail Youzhny of Russia yesterday, losing 3-6, 6-3, 7-6 (7-3), 4-6, 5-7. 

For women's singles, American tennis star Serena Williams is still in the running and is currently the top-ranked female in the field. Former No. 1 Victoria Azarenka of Russia, is still in the tournament, as is Li Na of China, who has consistently been making headlines since her first Grand Slam win at the French Open in 2011. Na won a tough match today against Ekaterina Makarova of Russia, winning the first set 6-4, but struggling in a tight second set, 6-7. However, Na pulled it out, dominating the third and final set, 6-2, and moving on the semis. 

Another person to watch is Carla Navarro of Spain, who is ranked 24th in the tournament but beat eighth-seeded Angelique Kerber in the fourth round the other day. 

There is definitely more to come in the upcoming days for the U.S. Open and as seen through history and recent match scores, anything can happen on the tennis court. Tennis gods have fallen and will continue to fall; and underdogs will get their moment to shine. 

Keep watching the U.S. Open to find out what happens next and who ultimately succeeds in winning the U.S. Open trophy. 

Reach Staff Writer Camille Requiestas via e-mail.