NEW YORK - Serena Williams didn't drop a game in advancing to the quarterfinals of the U.S. Open.

Williams beat 82nd-ranked Andrea Hlavackova 6-0, 6-0 in 57 minutes. It was the first time in 62 career victories at Flushing Meadows that the three-time U.S. Open champion enjoyed a "double bagel."

"She was fighting really hard," Williams said. "You give people any type of chance, especially in tennis, the match is never over until you shake hands. There is always a comeback available. So I didn't want to give her that opportunity — or anyone that opportunity — to try to come back, especially her in particular. She was getting so pumped up and she never gave up. I thought that was really incredibly positive."

Williams had 31 winners and just seven unforced errors. She and sister Venus play doubles during Monday's night session in Arthur Ashe Stadium.

Hlavackova, a 2011 French Open doubles champion, had never been past the second round in singles at a major tournament before this year.

Williams will next face Ana Ivanovic, who is finally back in a Grand Slam quarterfinal more than four years after her French Open title.

The 12th-seeded Serb beat Tsvetana Pironkova 6-0, 6-4. Ranked No. 1 in the world in 2008, Ivanovic has struggled with injuries and her confidence since.

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"There were some good moments and some tough ones, but it's a process. I understand it better now," she said. "There are times when you realize that it's exactly what it is: It's a process. You can't have everything at the same time. You have to be consistent on practice courts and then in the matches."

After failing to serve out the match at 5-3 in the second set, Ivanovic broke the 55th-ranked Bulgarian at love in the next game to clinch the victory.

Pironkova, a 2010 Wimbledon semifinalist, went up a break twice in the second set only for Ivanovic to immediately break back. There were seven service breaks in 10 games in the set.

Pironkova held serve just once in the match. Ivanovic had more success on Pironkova's first serve than her own. The Serb won 65 percent of the points when her opponent got in her first serve, compared with 61 percent when her own first serve landed in.

Italian doubles partners Sara Errani and Roberta Vinci each won to set up a meeting in the quarterfinals. Vinci upset second-seeded Agnieszka Radwanska 6-1, 6-4.