Former US Open champion Juan Martin del Potro has reached the second round of the competition with a straight-sets victory over Filippo Volandri.

Del Potro, who claimed the title at Flushing Meadows in 2009, defeated his Italian opponent 6-3 6-1 6-1 in the first round.

Injury has seen the Argentine slip down the rankings over the last year but he revealed after the match that he is now returning to his "best level".

"I keep improving very slowly," said the 22-year-old. "That's important. I think I'm serving much better than two years ago or at the beginning of this year.

"I know that other players are playing much better than me at this moment, especially the top 10 players. But to be here playing this tournament, for me it's a great signal for my future. I know I'm getting closer to my best level, and that's important."

Del Potro will now face fellow countryman Diego Junqueria in the next round.