Serena Williams moved within three wins of achieving a calendar-year Grand Slam by routing fellow American Madison Keys to set up a US Open quarter-final clash with sister Venus.
Williams beat the 20-year-old Keys 6-3 6-3 in 68 minutes to book a 27th professional career showdown with her older sister, who advanced with a 6-2 6-1 fourth-round victory over Anett Kontaveit (19) of Estonia.
Three-time defending champion Serena (right) holds a 15-11 advantage in the sisterly head-to-head series against Venus, splitting their four previous clashes at the US Open.
"She's playing great," 33-year-old Serena said about seven-times grand slam winner Venus, who is two years her elder. "I have to really be ready for that. At least one of us, a Williams, will be in the semis."
Serena, winner of 21 grand slam singles titles including this year's Australian Open, French Open and Wimbledon championships, would match Maureen Connolly (1953), Margaret Court (1970) and Steffi Graf (1988) should she win her seventh US Open crown.
Meanwhile, defending champion Marin Cilic was the first man through to the US Open quarter-finals, taking down France's Jeremy Chardy 6-3 2-6 7-6(2) 6-1.
Coming off a punishing five-setter with Mikhail Kukushkin in a third-round match that lasted four hours, Cilic took a while to find his power game but was unstoppable once he did, the ninth-seeded Croat blasting 23 aces past 27th seed Chardy, who had no answer.
"Key was finding my rhythm on the serve, especially towards the end of the third set," said Cilic. "But in the end it's pretty good."