Serena and Venus Williams will meet in the last 16 of the US Open after both won their third round matches at Flushing Meadows.
It will be the ninth Grand Slam meeting for the sisters, who both won in straight sets.
Eighth seed Serena booked her place first with a 6-3 6-4 victory over 25th seed Francesca Schiavone of Italy.
Elder sister Venus, seeded 10, then dispatched 20th seed Daniela Hantuchova of Slovakia 6-3 6-3.
Venus has been eclipsed by her younger sister since capturing consecutive US Open crowns in 2000 and 2001 but sensationally returned to form at Wimbledon this year, winning her fifth Grand Slam event.
Serena has admitted to being less than 50% healthy and lost the most recent match against her sister in Miami this year.
But she has won the last seven straight Grand Slam meetings with Venus since losing the first at the 1998 Australian Open.
It's extremely disappointing to have to play my sister in the next round, Serena said. Hopefully, one of us will be in the quarters, and we'll just have to go from there.
Kim Clijsters, the fourth seed, continued her momentum with a 6-1 6-4 victory over Japan's Ai Sugiyama in a match that lasted just 70 minutes.
Clijsters now faces a fourth-round clash against unseeded Israeli Shahar Peer, with the winner meeting the survivor of the battle of the Williams sisters.
Meanwhile, Maria Sharapova booked her place in the fourth round for the first time thanks to a 6-2 6-4 victory over Germany's Julia Schruff.
