Fourth-seeded Serena Williams easily advanced to the quarterfinals of the U.S. Open on Monday with a 6-0, 6-0 victory — what’s known as a “double bagel” — over 82nd-ranked Andrea Hlavackova of the Czech Republic. Williams will play 12th-seeded Serbian Ana Ivanovic, who advanced to a Grand Slam quarterfinal for the first time since 2008 by defeating 55th-ranked Tsvetana Pironkova of Bulgaria 6-0, 6-4. Tenth-ranked Sara Errani and Number 20 Roberta Vinci, both of Italy, will face each other in a quarterfinal match, after Errani downed sixth-seeded Angelique Kerber of Germany 7-6 (5), 6-3 and Vinci upset second-ranked Agnieszka Radwanska of Poland 6-1, 6-4. On the men’s side, top-seeded Roger Federer of Switzerland advanced to the quarterfinals without having to even get on the court, when his fourth-round opponent, 23rd-seeded Mardy Fish of the U.S., withdrew hours before their match on medical advice for precautionary reasons. Fish missed two-and-a-half months this season because of an accelerated heartbeat and had a medical procedure in May. Also advancing to the quarterfinals yesterday were Olympic gold medalist Andy Murray of Britain, Croatia’s Marin Cilic, and Tomas Berdych of the Czech Republic.