Serena Williams flawless in Round 4

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 -- who lost in doubles with older sister Venus on Monday night -- had 31 winners and just seven unforced errors.

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.

"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.

Doubles partners and best friends Sara Errani and Roberta Vinci will meet in a quarterfinal in a career year for both.

The Italians each advanced with an upset victory in straight sets. Vinci beat second-seeded Agnieszka Radwanska 6-1, 6-4 to make a Grand Slam quarterfinal for the first time. She ran to her box to celebrate after breaking the Pole's serve to end the match, tears in her eyes.

"I really had the worst day," said Radwanska, who could have moved up to No. 1 in the WTA rankings by reaching next weekend's final. "She really mixes it up -- a lot of slice, then suddenly hitting very well from the forehand side, then kick serve, drop shots, volleys as well, coming to the net. It's really tough because she really had an answer for everything."

The 20th-seeded Vinci had never been past the third round at a major tournament before Wimbledon this year.

Errani hadn't achieved that feat before 2012, either. Then she made the quarters at the Australian Open and the final at the French Open.

The 10th-seeded Errani defeated Angelique Kerber 7-6 (5), 6-3. She needed nearly 2 hours to win in two sets.

The two are still alive in doubles, in the quarterfinals as the No. 2 seed. They won the title at Roland Garros this year.

"Our friendship won't change, no matter what, no matter who wins," said Vinci, noting that she expects they'll have dinner together, as usual, Monday and Tuesday. "It definitely won't be an easy match from a mental perspective. We know each other well. We practice together often. We play doubles together. We know everything about each other."

Kerber made a surprise run to the U.S. Open semifinals a year ago and had advanced to at least the quarters at the French Open and Wimbledon in 2012. The sixth-seeded German double-faulted to end the first-set tiebreaker. She had 38 unforced errors.

When Kerber's final forehand bounced off the net cord and back, Errani dropped her racket and pumped both fists.

Radwanska, coming off a runner-up finish at Wimbledon, was trying to become the first Polish woman to reach the quarterfinals at this tournament in the Open era. She had been 4-0 against Vinci.

Radwanska could sympathize with Hlavackova's plight, having lost to Williams in the Wimbledon final.

"When she's on fire, you can't do anything about it. It doesn't matter what you try to do, it's going to be a winner," Radwanska said. "It's just Serena. She's a great champion."

Information from The Associated Press was used in this report.