NEW YORK -- No. 6 seed Alexander Zverev keeps playing five-set matches -- and keeps winning them. Frances Tiafoe? Not so much.
Zverev reached the third round of the US Open at Flushing Meadows with his second five-setter of the week, edging Tiafoe 6-3, 3-6, 6-2, 2-6, 6-3 on Thursday to improve to 5-0 in matches that go the distance in 2019.
Said Zverev: "It's usually what I do. The first few rounds at majors, I play five sets.''
It marked just the fourth time a top-10 seed at the US Open won a five-setter in each of his first two matches of the tournament.
Tiafoe, a 21-year-old American ranked 45th, dropped to 1-8 in fifth sets for his career.
That includes losses of that length in three of his past four US Opens.
Meanwhile, second-seeded Rafael Nadal advanced to the third round with a walkover after second-round opponent Thanasi Kokkinakis pulled out before their match with a right shoulder injury.
"I knew it was a possibility from this morning," Kokkinakis said. "I was feeling pain putting socks on. When you feel pain like that, it's not going to be easy hitting serves."
Kokkinakis said he was disappointed he had to pull out.
"Maybe my body isn't ready for five-set tennis," the Australian said. "Maybe I'm just not ready for Grand Slams yet. It's tough to swallow at the moment."
Kokkinakis, a wild card ranked No. 203, also retired from the first round of this year's Australian Open with the same injury.
Nadal's match at Arthur Ashe Stadium was replaced by a second-round contest between No. 22 Marin Cilic and Cedrik-Marcel Stebe that was previously scheduled for Louis Armstrong Stadium. Cilic, the 2014 champion, overcame 11 double faults with the help of 13 aces against Stebe and won 4-6, 6-3, 7-5, 6-3.
Cilic moves on to face American John Isner in a third-round matchup of big servers.
In other men's action, Nick Kyrgios had a relatively easy victory in his first match since saying the ATP was "corrupt,'' beating Antoine Hoang 6-4, 6-2, 6-4 to reach the third round.
The No. 28 seed wrapped up the match in just under two hours, a few minutes after briefly losing his temper when he thought Hoang was allowed to challenge a call too long after the point had ended. He argued with the chair umpire and then asked for an explanation from a supervisor, but got himself refocused and soon closed it out.
The ATP is considering whether to punish Kyrgios for a "major offense'' after his comments about the tour following his first-round victory. The ATP had fined him more than $100,000 for his behavior during a match last month, and in response to a question about it Krygios said the tour was "corrupt.'' He later sent out a tweet saying he had used an incorrect choice of words.
Earlier in the day, 15th-seeded David Goffin beat Gregoire Barrere 6-2, 6-2, 6-2 in less than an hour and a half. Stan Wawrinka, the 23rd seed, was pushed to a fourth set but defeated Jeremy Chardy 6-4, 6-3, 6-7 (3), 6-3 to reach the third round.
No. 5 seed Daniil Medvedev took down Hugo Dellien 6-3, 7-5, 5-7, 6-3 for his 46th tour-level match victory this season, the most by any player on the men's tour. Medvedev has been rolling this summer, having reached the finals at Washington and the Rogers Cup, and winning his first Masters 1000 title at Cincinnati.
No. 29 seed Benoit Paire surrendered a two-set lead to Aljaz Bedene and lost 4-6, 6-7 (3), 6-2, 7-5, 7-6 (4).
ESPN Stats & Information and The Associated Press contributed to this report.