World number two Rafael Nadal advanced to the US Open third round by walkover after Australian Thanasi Kokkinakis withdrew from the tournament with a right shoulder injury.
Rafael Nadal's US Open title path eased further on Thursday as he received a walkover into the third round while reigning Wimbledon champion Simona Halep crashed out early in New York for a third year running.
The Spanish 18-time Grand Slam winner advanced without striking a ball when injury-plagued Australian Thanasi Kokkinakis pulled out of their scheduled evening clash at Arthur Ashe Stadium with a right shoulder problem.
Nadal, the US Open champion in 2010, 2013 and 2017, will meet South Korean qualifier Chung Hyeon or Spanish 32nd seed Fernando Verdasco for a spot in the last 16.
His path to a fourth title, already helped with "Big Three" rivals Novak Djokovic and Roger Federer on the opposite side of the draw, cleared further having already seen four top-10 rivals dumped out in the first round.
Alexander Zverev, the sixth seed, is the highest-ranked player remaining on his side of the draw, as the German survived a second successive five-set marathon by outlasting American Frances Tiafoe 6-3, 3-6, 6-2, 2-6, 6-3 to equal his best US Open run.
"I've been here before. It's usually what I do in the first few rounds of majors, to play five sets," said Zverev, who has featured in 11 five-set matches at Grand Slams since the start of 2018 — more than any other player.
American world number 116 Taylor Townsend saved a match point to upend women's fourth seed Halep 2-6, 6-3, 7-6 (7/4), consigning the Romanian to another premature exit at Flushing Meadows, having been knocked out in the opening round in 2017 and 2018.
"I was not inspired at all today, but I fought. I thought when I came back that I will take it and I will win it. But sometimes it goes the other way," Halep said.
Halep strolled through the opening set but dropped serve twice to start the second set as Townsend, who had never beaten a top-10 player, leveled and then served for the match at 5-4 in the final set.
A double fault and a clutch Halep passing shot wiped out two match points for Townsend but the left-hander showed remarkable resolve, saving a match point down 5-6 and bossing the ensuing tie-break as she equaled her best run at a Grand Slam.
"This means a lot. It has been a long journey," said a tearful Townsend, who also reached the French Open third round on her Grand Slam debut in 2014.
Top seed Osaka proved too strong for 53rd-ranked Magda Linette of Poland, sweeping to a 6-2, 6-4 victory and setting up a potential showdown with 15-year-old American sensation Coco Gauff for a spot in the last 16.
"I feel like I had my moments where I played really well," Osaka said. "I think the main thing for me was that I was able to adjust whenever I figured out something was going wrong, so I think I'm heading in the right direction."
Kobe, Kaepernick in the crowd
Among the celebrities watching her match at Louis Armstrong Stadium were basketball legend Kobe Bryant and former NFL quarterback Colin Kaepernick, whose kneeling protest became a national symbol for champions of social justice and racial equality.
"I'm really grateful they came out," Osaka said. "It's really cool. I honestly just wanted to finish as fast as possible because I didn't want them to be out in the sun too long."
Osaka awaits the winner between teenager Gauff, the world number 140 who reached the fourth round in July at Wimbledon, or 112th-ranked Hungarian qualifier Timea Babos.
Men's fifth seed Daniil Medvedev, coming off a maiden Masters title in Cincinnati and runner-up finishes in Montreal and Washington, was struck down by cramp during a 6-3, 7-5, 5-7, 6-3 win over Bolivia's Hugo Dellien.
"I'm not sure what happened today and why I started cramping suddenly," Medvedev said. "I obviously thought at one point 'How did I win?' I don't know how I did."
Stan Wawrinka, the 2016 US Open champion, beat Jeremy Chardy in four sets and is on a fourth-round collision course with Djokovic.
Andrea Petkovic knocked out Czech sixth seed Kvitova 6-4, 6-4, while 15th seed Bianca Andreescu continued her steady progress with a 6-3, 7-5 win over Kirsten Flipkens.