Serena Williams and big sister Venus will meet in the quarter-finals of the US Open after the defending champion defeated fellow American Madison Keys.

Aiming for a calendar Grand Slam, Serena has dropped just one set on her way to the last eight, seeing off Keys 6-3 6-3 on Sunday.

Venus, who overcame Anett Kontaveit in just 52 minutes, will provide a stiff test for her sibling, but the Serena serve remains the most potent weapon in women's tennis.

To her credit, Keys did apply some early pressure, but the top seed always had an answer – usually in the form of an ace – when any serious questions were posed.

The world number one made the breakthrough in the eighth game of the first set, punishing a tame second serve to take a 5-3 lead before serving it out.

Keys, seeded 19th and competing in the fourth round at her home slam for the first time, saved break points in each of her first two service games in the second set as Serena continued to build pressure.

Ultimately that took its toll on Keys, who was broken in the seventh game and Serena did not look back from there, sealing the win in just over an hour to pave the way for a showdown with a very familiar face.

In 26 previous encounters, Serena has taken 15 wins against her older sibling, although it is two apiece in US Open contests.