No. 23 Mardy Fish was forced to pull out of the U.S. Open for "health concerns" on Monday afternoon. The American's withdrawal means that his opponent, top-ranked Roger Federer, moves on easily to his 38th consecutive Grand Slam quarterfinal.
"I regret that I have to withdraw from the US Open for precautionary measures," Fish said in a statement on the U.S. Open Website. "I was reluctant to do so, but am following medical advisement. I had a good summer and look forward to resuming my tournament schedule in the fall."
According to a Yahoo! Sports report, Fish had heart problems earlier this year when he was hospitalized for an elevated heart rate after an event in Miami and underwent a procedure to attempt to correct the issue.
Federer will face No. 6 Tomas Berdych in the quarterfinals after Berdych advanced with a 7-4, 6-4, 6-1 win over No. 11 Nicolas Almagro on Monday.
Both of the early women's matches at Arthur Ashe Stadium were easy victories for the higher seeds. No. 4 Serena Williams made short work of Andrea Hlavackova, winning 6-0, 6-0 in a match that lasted less than an hour. No. 12 Ana Ivanovic also advanced, easily beating Tsvetana Pironkova 6-0, 6-4 this morning.
There are two matches currently in progress. On the women's side No. 6 Angelique Kerber and No. 10 Sara Errani are in the second set with Errani leading 3-1 after taking the first set 7-6. On Arthur Ashe, No. 12 Marin Cilic leads Martin Klizan 2-1 in the first set.
For more on the 2012 U.S. Open, check out SB Nation's tennis hub. Head over to the official U.S. Open website for live scores.