Sock stuns Cilic; Djokovic, Nadal move up.

​New York: American tennis player Jack Sock upset 2014 champion Marin Cilic of Croatia in surprisingly routine fashion, breezing into the US Open pre-quarterfinals with a 6-4, 6-3, 6-3 victory, while big names Novak Djokovic and Rafael Nadal also progressed to the Round of 16.

The 26th-seeded Sock, who is known for his huge forehand and big serve but not for a stellar return game, on Friday broke Cilic's serve four times in three sets to win in one hour and 41 minutes at the Louis Armstrong Stadium.

Sock completely dominated his own service games, not facing a single break point in the contest.

Next up for the 23-year-old American will be ninth-seeded Frenchman Jo-Wilfried Tsonga, who moved into the fourth round with a 6-3, 6-4, 7-6 (7-4) victory over 23rd-seeded South African Kevin Anderson.

In another third-round men's singles result Friday, Serbian top seed and world No 1 Djokovic advanced to the Round of 16 for the 10th consecutive time in the US Open when Russia's Mikhail Youzhny retired with a leg injury while trailing 2-4 in the first set.

Djokovic, who moved into the third round with a walkover victory over Czech Jiri Vesely, is now in the "business end" of the tournament without much match practice.

He will next take on British up-and-comer Kyle Edmund, who dismissed huge-serving American John Isner 6-4, 3-6, 6-2, 7-6(5). Two-time US Open champion Nadal of Spain breezed past Russian Andrey Kuznetsov 6-1, 6-4, 6-2.

In the next round, the 30-year-old will face Frenchman Lucas Pouille, who edged past Spaniard Roberto Bautista Agut 3-6, 7-5, 2-6, 7-5, 6-1.

Mercurial 10th-seeded Frenchman Gael Monfils, who has been showing the best form of his career in recent months, moved into the fourth round with an emphatic 6-4, 6-2, 6-4 victory over Spain's Nicolas Almagro.

In the women's singles action, German Angelique Kerber, Denmark's Caroline Wozniacki, Italian seventh 7 seed Roberta Vinci, Britain's Johanna Konta and Czech Petra Kvitova all moved into the Round of 16 with comfortable victories.

World No 2 Kerber made quick work of qualifier American Catherine Bellis with a 6-1, 6-1 triumph to book a place in the fourth round, where she'll play former No.2 Kvitova, who moved past Ukranian Elina Svitolina 6-3, 6-4.

In pole position to become the first German to become No 1 in the world since Stefanie Graf in 1997, the reigning Australian Open champion put on a masterclass for Bellis, the tournament's most impressive young talent.

Kerber proved a bridge too far for Bellis as the German hit 17 winners to 18 unforced errors, not only dictating play but also playing the cleaner match compared to Bellis.