The many courts at USTA Billie Jean King National Tennis Center were a beehive of activity on Saturday, with 42 matches contested on Day 6 of the 2013 U.S. Open.
Rafael Nadal and Victoria Azarenka looked sharp and moved on to the next round, but Petra Kvitova and John Isner weren't so lucky.
Most of the world pays attention to the men's and women's singles draws, but there was a noteworthy development on Saturday that headlines the biggest surprises from Day 6.
Note: For a full list of results, please refer to USOpen.org.
The Williams Sisters Score a Major Upset
Serena Williams, who has been dominant in the women's draw thus far, scored a major upset when she and sister Venus Williams defeated the No. 7-seeded duo of Rachel Kops-Jones and Abigail Spears, as noted by the event's official Twitter account:
It's not often that Serena Williams is associated with an upset, but it was a pretty big deal for the un-seeded Williams sisters to win this match.
The final score was 6-4, 6-4.
Interestingly enough, the team of Williams and Williams struggled with mistakes throughout the match, with nine double faults and 23 unforced errors. In the end, Venus and Serena used their outstanding athleticism, range and power to overcome their shortcomings.
It won't get easier for them in Round 4, as the No. 11-seeded duo of Anastasia Pavlyuchenkova and Lucie Safarova will be standing in the way of advancement.
Petra Kvitova Suffers an Early Exit
Since winning the 2011 Wimbledon Championship, Kvitova hasn't been able to get past the semifinals in any Grand Slam event, and she won't be breaking the streak at the U.S. Open this summer.
The No. 7 player in the world kept a different streak alive, failing to get out of the fourth round at Flushing Meadows for the sixth straight year.
American Alison Riske took control of the match early, taking the first set 6-3 before putting her foot on the gas pedal in a big way. Finishing off her opponent in style, Riske won the second set 6-0.
Kvitova didn't even get a single break-point opportunity, while Riske converted five of nine attempts.
As noted by Ben Rothenberg of the New York Times, this is Riske's first appearance in the top 16 of a Grand Slam event, making this upset all the more special:
Alison Riske def No7 Petra Kvitova 6-3, 6-0. Kvitova nowhere near at her best, obviously, but an impressive first Slam R16 for Ali. #usopen— Ben Rothenberg (@BenRothenberg) August 31, 2013
John Isner Falls to Philipp Kohlschreiber
Though not a huge upset, Kohlschreiber's victory over Isner was not expected.
After splitting the first two sets, the German would not be denied the victory. As noted by the event's Twitter account, he won the final two sets by the slimmest of margins, 7-5, 7-6(5):
Not surprisingly, Isner dominated the court with his serve at times. The lanky power specialist registered 26 aces against his opponent, but he also made plenty of mistakes with five double faults and a whopping 40 unforced errors.
A clear illustration of just how close the match was, both players scored 123 points.
In the end, Isner's mistakes were the difference.
Now Kohlschreiber will have the dubious honor of taking on Rafael Nadal in Round 4, and he'll need to step up his game a few notches to record another upset.
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