Roger Federer and Maria Sharapova will take center stage at the U.S. Open on Friday but Flushing Meadows is slowly turning into a Williams family affair with the sisters eager to add to their grand slam collections.

With seven U.S. Open singles titles between them, Venus and Serena have both set their sights on the Sept. 7 women's final but have also joined forces in an effort to take the doubles crown as well.

Venus will try to show younger sister Serena the way into the fourth round when she takes on 13th seeded Italian Sara Errani in an early matchup on Arthur Ashe Stadium court.

"She's a great singles player and a doubles player," said Williams, who claimed back-to-back U.S. titles in 2000 and 2001.

"Every time I've played her, I've had to be focused on every single point because she does not let up on any point no matter what the score is.

"If she's down 5-Love, 40-Love and never won a game in the match, she is in there still to win the match. That's my main thing: to stay focused and play my game."

Sharapova, another former U.S. Open champion, will meet Germany's Sabine Lisicki while China's Peng Shuai, who beat fourth seed Agnieszka Radwanska, will face off against Italy's Roberta Vinci.

Second seed Federer, a five-time U.S. Open winner, will take on Australia's Sam Groth for a spot in the third round as he continues his bid to add to his record haul of 17 grand slams.

Fourth seed David Ferrer of Spain will also face Australian opposition when he battles Bernard Tomic in a second round clash.

(Editing by Greg Stutchbury)