Monday's action in Flushing Meadows was exciting and gave us a few surprises, as competitors do their best to be the 2012 U.S. Open Champion.
The matches are less frequent, but that doesn't mean it's lower quality. In fact, it's the opposite.
With each side of the draw entering quarterfinal action, we are starting to find the real contenders. After Andy Murray's victory over Milos Raonic in the day's final match, he looks like a solid contender to Roger Federer and Novak Djokovic.
The day's two biggest moments came with Mardy Fish's shocking withdrawal from the tournament, prior to his match against Federer and Agnieszka Radwanska's surprising loss to Roberta Vinci.
Let's take a look at the day's results and highlight a few key moments.
*For Monday's full results, click here
Marin Cilic (12) def. Martin Klizan 7-5, 6-4, 6-0
Roger Federer (1) def. Mardy Fish (23) (Fish withdrew)
Tomas Berdych (6) def. Nicolas Almagro (11) 7-6 (4), 6-4, 6-1
Andy Murray (3) def. Milos Raonic (15) 6-4, 6-4, 6-2
Ana Ivanovic (12) def. Tsvetana Pironkova 6-0, 6-4
Serena Williams (4) def. Andrea Hlavackova 6-0, 6-0
Sara Errani (10) def. Angelique Kerber (6) 7-6 (5), 6-3
Roberta Vinci (20) def. Agnieszka Radwanska (2) 6-1, 6-4
Fish Withdraws for Health Reasons
Fish was supposed to face Federer in Round 4 action on Monday, but he withdrew prior to the match for precautionary reasons.
The Associated Press (via the Washington Post) notes that Fish missed over two months this season for an accelerated heartbeat. That's not a situation to take lightly, and Fish was wise to heed his doctor's advice on Monday.
Nonetheless, it gave the day an unforeseen twist. This was supposed to be a relatively competitive match, but Federer will move on to face Tomas Berdych in the quarterfinals instead.
Serena Williams Dominates
Williams hadn't dropped a single set at Flushing Meadows thus far, but Monday's performance was almost unfair. She dominated Hlavackova, and threw up a "double doughnut."
She hit 31 winners. Her serve wasn't exactly on point, but her seven unforced errors was her lowest total in the tournament so far.
Williams will face Ivanovic in the quarterfinals. Both players are playing well, but Williams has been on a different level this summer.
Radwanska Makes an Early Exit
This is the biggest upset of the tournament so far. Vinci isn't a bad player, but Radwanska was the No. 2 seed in the women's draw.
Coming into this match, Radwanska was playing reasonably well. She dropped on set to Carla Suarez Navarro in the second round, but she was unblemished otherwise.
We knew something like this would happen at some point, but the first major upset is always worth noting.
Vinci will face No. 10 seed Errani in the quarterfinals.