Novak Djokovic continued to look the man to beat at the US Open as he cruised into the fourth round with a routine win over American Sam Querrey.

Djokovic has not been tested in any of his matches so far and needed just an hour and 25 minutes to dispatch Querrey 6-3 6-2 6-2.

Querrey's serve is his biggest asset but Djokovic was all over it, the American winning just 23 per cent of points on his second serve and only 57 per cent on his first.

Coming into the tournament, Djokovic admitted he did not know how being away from his pregnant wife would affect him but any rivals looking for a lack of focus will have been sorely disappointed.

Andy Murray had another frustrating afternoon on the Louis Armstrong Stadium court but did enough to defeat Andrey Kuznetsov.

There was not the same drama as there had been in round one, when he cramped against Robin Haase and might have lost, but Murray again found himself embroiled in a fight having appeared in total control against a player ranked 96th in the world.

He at least finished the match relatively strongly, recovering from dropping the third set to clinch a 6-1 7-5 4-6 6-2 victory after two hours and 35 minutes.

Much stiffer tests lie ahead though, with Jo-Wilfried Tsonga his likely next opponent.

Fifth seed Milos Raonic ended the run of Victor Estrella Burgos in a tight match that was decided by three tie-breaks.

Estrella Burgos' rise into the top 100 at the age of 34 has been one of the best stories of the season but even his enthusiastic band of fans could not propel him to victory this time as the Canadian prevailed 7-6(7/5) 7-6(7/5) 7-6(7/3).

In the fourth round Raonic will play 10th seed Kei Nishikori, who came into the tournament short on matches because of injury but has been impressive and beat Leonardo Mayer 6-4 6-2 6-3.

Tommy Robredo ended the run of 19-year-old Nick Kyrgios with a masterclass of experience versus youth.

Australian Kyrgios is made for a stage like Arthur Ashe under the lights and powered his way into a 5-0 lead.

But Robredo is one of the canniest players around and he worked away at Kyrgios' raw edges to turn the match in his favour and win 3-6 6-3 7-6 (7/4) 6-3.

Robredo beat Roger Federer in the fourth round last year and will attempt to upset another Swiss, third seed Stan Wawrinka, in the last 16 this time.