World number one Novak Djokovic has eased into the second round of the US Open with an efficient 6-1 6-2 6-2 victory over Lithuania's Ricardas Berankis on Arthur Ashe.

The Serbian, last year's beaten finalist, was not at his absolute best - Berankis created eight break-point opportunities - but nevertheless had far too much for his 23-year-old opponent, seeing him off in an hour and 22 minutes.

Berankis gave the crowd hope they may see a contest by producing a cross-court pass to take the first point of the match, but Djokovic asserted his authority to hold, then broke immediately and ominously.

Berankis was on the brink in his next service game too, but saved a break point via a Hawkeye challenge on a backhand down the line and held to get on the board.

Djokovic broke again in game six though and, despite facing a couple of break points himself, he served out the set.

And there was more of the same in the second set as Berankis simply could not deal with the depth and power of the Djokovic groundstrokes.

Djokovic powered through the set and when he served out to love with another huge forehand, the match was less than 50 minutes old.

Berankis was up against it from the off in the third as he was broken in game one, then threw away a chance on the Djokovic serve by powering a forehand return long.

When the Lithuanian dumped an overhead into the net to give the world number one a 4-0 lead it was symptomatic of his inability to take the chances that came his way, although he was able to finish with a flourish by finally breaking in game six.

Djokovic powered on though and took the next two games to seal a second-round match-up with Benjamin Becker.

Roger Federer was relatively untroubled as he eased through to the second round with a straight-sets victory over Grega Zemlja.

The five-time champion is in the unusual position of being only the seventh seed after his poor season and is no longer considered in the same bracket as Novak Djokovic, Rafael Nadal or Andy Murray in terms of being a title favourite.

But there were signs in Federer's narrow loss to Nadal in Cincinnati last week that some of the old magic has been dormant, rather than dead.

After testing a larger-headed racket following his shock Wimbledon loss to Sergiy Stakhovsky, Federer has returned to the racket that brought him 17 grand slam titles.

He also insisted prior to the start of the tournament that the back issues that have plagued him were behind him, and he did not appear to have many problems in a 6-3 6-2 7-5 win over Zemlja.

The match was supposed to be played in the night session last night but rain began to fall just before they were due to go on court.

The only blip as far as Federer was concerned came when he gave up break points for the first time in the eighth game of the third set and Zemlja took his third chance.

But Federer broke again to lead 6-5 with a rasping forehand winner and this time made sure there was no way back for his Slovenian opponent.

The 32-year-old next meets Argentina's Carlos Berlocq, who was also affected by rain last night, but it worked in his favour as he fought back from two sets to one down to defeat Santiago Giraldo.

The tournament lost two of tennis' rising stars in the first round as Grigor Dimitrov and Jerzy Janowicz were sent packing.

Dimitrov, the 25th seed, is yet to live up to his talent, with some standout victories accompanied by baffling losses.

This fell into the latter category, with the 22-year-old Bulgarian going down 3-6 6-3 6-4 5-7 6-2 to world number 95 Joao Sousa.

Dimitrov, whose best performance in a grand slam is a third-round appearance at the French Open this year, twice fought back from a break down in the fourth set but was outplayed in the decider.

Janowicz's 6-4 6-4 6-2 defeat by Argentinian Maximo Gonzalez was even worse on paper but he was hampered by a back injury that took away the power of his fearsome serve.

Janowicz called the trainer onto Court 13 during the second set and, although he recovered from 4-1 to 4-4, there was no way back.

The 14th seed would have hoped to do damage here after reaching the semi-finals at Wimbledon and his exit along with that of Ernests Gulbis yesterday makes a wide open third section of the draw even more so.

Milos Raonic is also in that section and he must fancy his chances of going a long way.

The Canadian 10th seed, who reached the Masters series final in Montreal earlier this month, beat Italian qualifier Thomas Fabbiano 6-3 7-6 (8/6) 6-3.

Fifth seed Tomas Berdych, who took out Federer last year, could be a threat in the tournament and he was an impressive 6-1 6-4 6-1 winner over Paolo Lorenzi of Italy.

Thirteenth seed John Isner is the main American hope and he thrashed Filippo Volandri 6-0 6-2 6-3 - not too surprising considering the Italian has not won a Tour-level match on hard courts since 2008.

American qualifier Donald Young hammered Martin Klizan, who beat Jo-Wilfried Tsonga here last year, for the loss of just two games while there were also wins for Gael Monfils, Tommy Haas and Sam Querrey but 15th seed Nicolas Almagro lost in four sets to Denis Istomin.