New York - Roger Federer and Andy Murray coasted into the US Open fourth round Saturday as Canadian poster girl Eugenie Bouchard suffered a potentially tournament-ending head injury in a freak fall.
Five-time champion and world number two Federer claimed a 6-3, 6-4, 6-4 victory over Philipp Kohlschreiber, his 10th win in 10 meetings against the 29th-ranked German.
Murray, seeded three and the New York champion in 2012, brushed aside Thomaz Bellucci of Brazil 6-3, 6-2, 7-5 for his 40th career win at the US Open.
Federer, 34, hoping to become the oldest champion since Ken Rosewall in 1970, will next face US 13th seed John Isner, who progressed after Czech opponent Jiri Vesely retired with a neck injury after dropping the first two sets.
Federer has now reached the fourth round in New York for the 15th year as he looks to return to the final for the first time since 2009.
"I won the big points today, I served well when I had to, even though it was up and down for both of us," said Federer, who will take a 4-1 career lead over Isner into their fourth-round clash.
Murray had needed to rally from two sets down to see off France's Adrian Mannarino in the second round.
But despite falling a break down in the first set on Saturday, he eventually breezed to victory over the 30th-ranked, left-handed Bellucci.
Murray, who has advanced to the quarter-finals or better at his last 18 Grand Slams, next faces South Africa's 15th seed Kevin Anderson.
Anderson has never gone beyond the fourth round at a major and trails Murray 4-1 in career meetings including two clashes this year.
The big South African, boosted by a title on the hard courts of Winston Salem last weekend, made the last 16 with a 6-3, 7-6 (7/3), 7-6 (7/3) win over Austria's Dominic Thiem.
"It was much slower conditions today which made it tough to serve but easier to return so there were a lot of long rallies," said Murray.
"He got the early break but I got it back straightaway, used my variety and made it tough for him."
Bouchard was facing a battle to make her scheduled last-16 clash with Italy's Roberto Vinci on Sunday after injuring her head in a fall in the women's locker room on Friday.
The 21-year-old Canadian withdrew from the women's and mixed doubles tournament on medical advice.
Organisers had been due to update her status late Saturday but also scheduled Bouchard to play last on Louis Armstrong Stadium on Sunday to maximise her chances of taking part.
Two-time runner-up Victoria Azarenka, the 20th seed, triumphed over 11th-seeded German Angelique Kerber in an Arthur Ashe Stadium thriller lasting almost three hours.
Azarenka, whose season has been blighted by a left thigh injury, won 7-5, 2-6, 6-4 on a sixth match point having trailed 2-5 in the first set.
The 26-year-old took her record over Kerber to 5-0 on the back of 51 winners to her opponent's 46 in a merciless contest of big-hitting.
Both players saved a combined 26 break points before the Belarusian prevailed to set-up a last-16 clash with America's Varvara Lepchenko.
"Angelique is a great fighter but I enjoy the hustle and getting winners and chasing down every ball," said two-time Australian Open champion Azarenka.
Fifth seed Stan Wawrinka, the French Open champion, made the last 16 with a 6-3, 7-6 (7/5), 6-4 win over Belgian world number 107 Rubens Bemmelmans.
Wawrinka goes on to face unseeded American Donald Young, who pulled off his second comeback from two sets to love down to beat Serbian 22nd seed Viktor Troicki 4-6, 0-6, 7-6 (7/3), 6-2, 6-4.
Czech sixth seed Tomas Berdych, a semi-finalist in 2012, reached the last 16 for a fourth successive year by beating Spain's Guillermo Garca-Lopez 6-7 (2/7), 7-6 (9/7), 6-3, 6-3.
He next plays 12th seed Richard Gasquet, one of four Frenchmen in the last 16, who defeated Australia's Bernard Tomic 6-4, 6-3, 6-1.
Romanian second seed Simona Halep reached the last 16 with a 6-2, 6-3 win over American qualifier Shelby Rogers.
Next up for Halep is Germany's 24th seed Sabine Lisicki, who came back from 1-5 down in the final set to defeat Barbora Strycova of the Czech Republic 6-4, 4-6, 7-5 before collapsing to the floor in floods of tears.
Two-time Wimbledon winner Petra Kvitova, the Czech fifth seed, eased past Anna Karolna Schmiedlova of Slovakia 6-2, 6-1.
She next faces British qualifier Johanna Konta, the world number 97 who beat German 18th seed Andrea Petkovic 7-6 (7/2), 6-3.
Samantha Stosur, the 2011 champion and the last woman to beat Serena Williams at the tournament, battled past Italy's Sara Errani 7-5, 2-6, 6-1.
Next for Stosur is another Italian, 26th seed Flavia Pennetta, a 2013 semi-finalist, who put out world number 149 Petra Cetkovska 1-6, 6-1, 6-4.