Defending champion Serena Williams won impressively against Vania King, as runner-up Victoria Azarenka defeated Christina McHale and they advanced to the third round of the U.S. Open on Thursday.

World No. 1 Williams powered her way over King and with not so favorable windy conditions. She served up four service aces and 25 winners to finish the 25-year-old Taiwanese-American in just 56 minutes, 6-1, 6-0.

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Since the start of the tournament, Williams, 32, has fought off fellow Americans. The first was teen Taylor Townsend whom she demolished, 6-3, 6-1, and now King.

The 17-time Grand Slam champion Williams will now face another American Varvara Lepchenko in the third round.

Last year's U.S. Open finalist Azarenka also won against American McHale in just two sets, 6-3, 6-2, but the match took a lot of rallies, and conditions were not favorable for both players causing some delays.

The match lasted an hour and 46 minutes, with the Belarusian converting 23 winners and making all 24 net points.

"It took me a little bit of time to get into rhythm," Azarenka said. "Conditions weren't really easy. I think also I needed a little bit of a moment to adjust."

The two-time Australian Open champion Azarenka will go up against Russian Elena Vesnina in the next round.

Wimbledon champion Petra Kvitova defeated fellow Czech Petra Cetkovska, 6-4, 6-2, in an hour and 27 minutes delivering 23 winners compared to only six from Cetkovska.

Kvitova, 24, will be facing Serbian qualifier Aleksandra Krunic, who upset 27th seed American Madison Keys in an earlier match, 7(7)-6(4), 2-6, 7-5.

Both Kvitova and Azarenka are on the same section, and if they both win against their opponents in the third round, they will face each other in the fourth round.

Two former Grand Slam champions were upset Thursday 2011 U.S. Open champ Samantha Stosur was defeated by Kaia Kanepi of Estonia and 2008 French Open winner Ana Ivanovic lost to Czech Republic's Karolina Pliskova.

TagsSamantha Stosur, Ana Ivanovic, serena williams, Victoria Azarenka, Petra Cetkovska