US Open PHOTOS: Venus, Serena to face off in quarters; Djokovic stretched

Defending champion Marin Cilic goes through to quarters; Canadian Eugenie Bouchard out with concussion

Get ready for the Williams Family show at the US Open as Venus and Serena will face off in the quarter-finals, in what is billed as one of the biggest matches of the tournament.

Venus Williams stands in the way of younger sister Serena's bid for a calendar-year Grand Slam after reaching the quarter-finals with a 6-2, 6-1 rout of Estonian teenager Anett Kontaveit on Sunday.

Seven-time grand slam winner Venus will face top-seeded world number one Serena in the last eight, after the three-time defending US Open champion won her fourth-round match 6-3, 6-3 against fellow American Madison Keys in 68 minutes.

The 35-year-old Venus, seeded 23rd, overpowered 19-year-old qualifier Kontaveit, winning 84 percent of her first serves, breaking the Estonian four times and making only nine unforced errors in the 50-minute match.

Serena, 33, is trying to become the fourth woman to sweep all four grand slam singles titles in the same year after winning the Australian Open, French Open and Wimbledon this season.

"She's playing great," 33-year-old Serena said about 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."

Top seed Novak Djokovic was made to work hard by Spain's Roberto Bautista Agut before he posted a 6-3, 4-6, 6-4, 6-3 win at the US Open on Sunday, moving him into his 26th consecutive grand slam quarter-final.

After Djokovic won an opening-set groundstroke battle with steady accuracy and well chosen forays to the net, Bautista Agut used his big forehand to come back from 4-2 down in the second and win the next four games to level the match.

The world number one smashed his racquet after losing the second set but made better use of its replacement, winning the third following a service break in the fifth game, before raising his performances in the fourth set to claim victory.

"Congratulations to Bautista for hanging in there, for fighting. It was a great match tonight," said the Serb, winner of this year's Australian Open and Wimbledon titles.

The Spaniard unleashed 34 winners, including 22 from the forehand, but came up short in a quest to reach his first grand slam quarter-final.

"He made me work for every point," said Djokovic, who will meet Spain's Feliciano Lopez, who beat Italy's Fabio Fognini 6-3, 7-6(5), 6-1, in the quarter-finals.

Only Jimmy Connors (27) and Roger Federer (36) have registered more consecutive grand slam quarter-final appearances in the Open era.

Defending champion Marin Cilic kicked off centre court action on another sunny day at the National Tennis Centre and was the first man through to the last eight, taking down determined Frenchman Jeremy Chardy 6-3, 2-6, 7-6(2), 6-1 to extend his Flushing Meadows win streak to 11 matches.

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 today was finding my rhythm on the serve, especially towards the end of the third set," said Cilic.

"I played really good in the fourth set, really great tennis, so I’m happy about it."

After splitting the opening two sets, Cilic's power began to show through, particularly in the third set tiebreak when he used his big serve to full advantage firing four aces and going up 6-1 before closing out 7-2.

Four Frenchmen made the round of 16, a US Open record, and at least one advanced to the quarter-finals, with Jo-Wilfried Tsonga beating countryman Benoit Paire 6-4, 6-3, 6-4.

Canadian 25th seed Eugenie Bouchard has withdrawn from the U.S. Open after suffering a concussion in a locker room fall, tournament officials said on Sunday.

"Eugenie Bouchard is withdrawing from the women's singles competition at the 2015 U.S. Open due to concussion," tournament director David Brewer said in a statement.

A Wimbledon finalist in 2014, Bouchard suffered the injury on Friday when she slipped and fell in the locker room and had already pulled out of doubles and mixed doubles matches scheduled for Saturday.

Bouchard had been scheduled to meet Italy's Roberta Vinci in a fourth-round match on Louis Armstrong Stadium court on Sunday.