Serena and Venus Williams advanced to a dramatic US Open quarter-final showdown with straight-set triumphs while Canada's Eugenie Bouchard withdrew from her fourth-round match due to a concussion.
World number one Serena Williams served well in moving within three match victories of a rare calendar Grand Slam with a 6-3, 6-3 triumph over US 19th seed Madison Keys last night.
Serena made only six unforced errors to 19 for Keys and hit 58 percent of her first serves. She took 79 percent of those points and 70 percent on her second serves, nearly twice Keys' second-try effectiveness.
"I'm so proud. I'm so glad it's so much better," Serena said of her serve.
"My only chance was to start out fast. I just stayed in there and was able to relax."
Venus, seeded 23rd, downed 152nd-ranked Estonian teen qualifier Anett Kontaveit 6-2, 6-1 at Arthur Ashe Stadium, matching her deepest Grand Slam run since reaching the 2010 US Open semi-finals.
"We're both prepared," Venus said. "Even though you're playing your sister you have to be prepared and focus. The preparation doesn't change."
Serena, who holds all four major tennis titles, is trying to complete the first calendar Grand Slam since Steffi Graf in 1988 and match Graf's Open Era record of 22 career Slam singles titles by capturing her Open Era record seventh US Open crown.
But Venus, two years older than Serena at 35, could play the spoiler as she tries to add to a trophy collection that includes the 2000 and 2001 US Opens and five Wimbledon titles, the most recent in 2008.
"I don't think anyone wants to be a spoiler. I think people love to see history being made," Venus said.
"But at the same time, you're focused on winning your match even though the circumstances are really much different than you."
Bouchard, who suffered a head injury after slipping in the locker room late Friday, pulled out of her match against Italy's Roberta Vinci with what US Open tournament director David Brewer said was a concussion.
Bouchard had pulled out of mixed and women's doubles on Saturday.
The 21-year-old from Montreal was a French and Australian Open semi-finalist last year and lost the 2014 Wimbledon final to Petra Kvitova.
Her head injury to a season of setbacks, including first-round French Open and Wimbledon exits and a 12-17 record.
