Novak Djokovic racked up his 60th win of the year yesterday to join former champions Serena Williams and Roger Federer in the US Open last 16 as Flushing Meadows claimed a record 18th injury victim.

World number one Djokovic, who has lost just twice in 2011, clinched a 6-3, 6-4, 6-2 victory over Russia's Nikolay Davydenko to set up a fourth round meeting with Ukraine's Alexandr Dolgopolov.

Djokovic, the Australian Open and Wimbledon champion, had only dropped three games in his first two rounds, but wily Davydenko, a semi-finalist in 2006 and 2007, gave the Serb a decent workout under the lights of Arthur Ashe Stadium.

"I played well at important moments and got the crucial breaks in all three sets," said the top seed.

"He was aggressive and stayed close to the lines. But I was passive and I wasn't happy with the game."

Williams, who missed last year's tournament at the start of an 11-month injury and life-threatening illness lay-off, defeated Belarusian fourth seed Victoria Azarenka 6-1, 7-6 (7/5).

The 13-time Grand Slam champion, seeded a lowly 28, next faces former world number one Ana Ivanovic of Serbia who saw off US wildcard Sloane Stephens 6-3, 6-4.

In a tournament missing defending champion Kim Clijsters, and which saw Maria Sharapova, French Open champion Li Na and Wimbledon winner Petra Kvitova all fail to reach the second round, Williams looks the hot favourite.

Asked what it felt like to be blitzed 5-0 after just 17 minutes of the first set, Azarenka said: "It's painful."

Williams, who saw three match points slip away in the ninth game of the second set, insisted she still has much to work on.

"I think in the first set I played some really good tennis. In the second, she kind of dictated. I probably could have played better."

Federer reached the fourth round for the 30th consecutive time at a Grand Slam with a 6-3, 4-6, 6-4, 6-2 win over Croatia's 27th seed Marin Cilic.

The third-seeded Swiss next plays Argentina's Juan Monaco who defeated Tommy Haas 6-7 (3/7), 6-3, 6-2, 6-3 with the German veteran committing a huge 71 unforced errors.

"It was a tough match. Coming in I knew it was going to be tricky, and I'm happy that I was able to counter his pace and his good play," said Federer.

Wozniacki, the runner-up to Clijsters in 2009, and still searching for an elusive first Grand Slam title, made the last 16 with a 6-2, 6-4 victory over America's world number 103 Vania King.

The Dane next faces 15th-seeded Russian Svetlana Kuznetsova, the 2004 champion, who eased past Uzbekistan's Akgul Amanmuradova 6-4, 6-2.

Meanwhile, Czech ninth seed Tomas Berdych and Marcel Granollers, the Spanish 31st seed, took the tournament injury toll to a record 18 when they quit their third round matches.

Berdych was suffering from a right shoulder injury and needed treatment at the end of the first set against Serbia's Janko Tipsarevic, which he lost 6-4, and then called it quits when he was down 5-0 in the second.

Granollers was trailing Spanish compatriot and 2003 runner-up Juan Carlos Ferrero 6-1, 4-3 when he brought proceedings to a halt with a stomach strain.

Tipsarevic and Ferrero will meet for a quarter-final place.

"For me it is shocking to see so many retirements," said Federer, who has conceded just one walkover in his 973-match career.

"It doesn't matter how bad I'm feeling, I will be out there and giving it a try, because you never know what's going to happen."

Also going through on Saturday was 2010 French Open champion Francesca Schiavone, the Italian seventh seed, who saved a match point before defeating South Africa's Chanelle Scheepers 5-7, 7-6 (7/5), 6-3.

Schiavone next faces Russian 17th seed Anastasia Pavlyuchenkova who beat Serbian 11th seed Jelena Jankovic, the 2008 runner-up, 6-4, 6-4.

German 10th seed Andrea Petkovic made the last 16 for the second successive year with a 6-4, 6-0 win over Italian 18th seed Roberta Vinci 6-4, 6-0.

She will play Carla Suarez Navarro, who put out fellow Spaniard Silvia Soler-Espinosa 6-0, 6-4.

Men's eighth seed Mardy Fish defeated South Africa's Kevin Anderson 6-4, 7-6 (7/4), 7-6 (7/3) and next plays French 11th seed Jo-Wilfried Tsonga who saw off Fernando Verdasco, the 19th-seeded Spaniard, in straight sets.