Persistent showers at the US Open have forced Roger Federer's first-round clash with Grega Zemlja to be postponed until day two of the tournament.

Federer was due to take on Zemlja in the last match on day one of the season's final Grand Slam, finishing a night session on the Arthur Ashe court.

Before the match could begin a shower arrived in New York and stubbornly refused to leave, forcing organisers at Flushing Meadows to make Federer and Zemlja return tomorrow.

The decision means that fans on Arthur Ashe got to see just 13 games in the first night session of the tournament, as defending women's champion Serena Williams beat Francesca Schiavone in straight sets.