Serena Williams didn't drop a game Monday as she moved into the quarterfinals of the USOpen. Roger Federer advanced with even less work when Mardy Fish pulled out of their fourth-round match for precautionary reasons.
Fish missed about two months this season because of an accelerated heartbeat and had a medical procedure in May. Fish's agent said he wasn't sure if the problem related to his previous health issues.
"I was reluctant to do so, but am following medical advisement," Fish said about his withdrawal in a statement. "I had a good summer and look forward to resuming my tournament schedule in the fall."
The 30-year-old American's third-round match against Gilles Simon went five sets, lasting more than 3 hours and ending after 1 a.m. Sunday. Afterward, the 23rd-seeded Fish did not appear at a news conference. Tournament officials said he was getting treatment, but didn't give specifics.
"I am really sorry for Mardy. I just want to wish him a speedy recovery," Federer said in a statement. "We all want to see him back on tour soon."
Federer, in his 34th consecutive quarterfinal at a major tournament, will meet sixth-seeded Tomas Berdych, who defeated 11th-seeded Nicolas Almagro 7-6 (4), 6-4, 6-1.
No. 12 Marin Cilic of Croatia put together a 7-5, 6-4, 6-0 victory over 50th-ranked Martin Klizan of Slovakia, the last left-hander and unseeded man remaining in the draw, and will take on the winner of Monday night's match between London Olympic gold medalist Andy Murray and No. 15 Milos Raonic of Canada.
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 won a match without losing a game.
"She was fighting really hard," Williams said. "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 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 were to play doubles during Monday's night session in Arthur Ashe Stadium.
It didn't take long for Serena Williams to show Hlavackova where things were headed.
"The first point of the whole match," Hlavackova explained, "when I served, and she returned, like, a 100 mph forehand return, I was like, 'OK, I know who I'm playing. You don't have to prove it to me. I know.'"
Monday's match was less than 15 seconds old. It might as well have been over.
Dominant from the moment she ripped that return of an 88 mph (142 kph) second serve, forcing Hlavackova into an out-of-control backhand that sailed well long, to the moment she powered a 116 mph (187 kph) service winner on the last point.
Hlavackova, a 2011 French Open doubles champion, had never been past the second round in singles at a major tournament before this year.
"My coach warned me to not go on the court and play for a score," Hlavackova said, by which she meant just trying to keep it as close as possible. "I was in the match. I was trying to figure out how to win. And when it was, like, 6-love, 4-love, 30-love, I was thinking, 'Well, I'm not playing for a score, but one game wouldn't hurt.'"
Williams — who lost in doubles with older sister Venus on Monday night — will next face former No. 1 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.
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.