Rafael Nadal returned from an extended rest to cruise into the US Open last 16 on Saturday, while Alexander Zverev again battled through.
Second seed Nadal, a three-time winner at Flushing Meadows, disposed of 170th-ranked South Korean qualifier Chung Hyeon 6-3, 6-4, 6-2, having benefited from three days off after a second-round walkover.
The Spaniard improved his record in New York against players outside the top-50 to 35-1 and will meet 2014 champion Marin Cilic for a place in the quarter-finals.
"I'm happy to be in the fourth round for one more time. It was a good match," said Nadal, who quit with injury against Juan Martin del Potro during last year's semi-final. "I'm trying to play a little bit more aggressive and a little bit less than before."
"It's true last year I had some tough matches. You never know what's better or worse," he said of his serene progress this week.
Cilic, the 22nd seed and 2017 Wimbledon finalist, took out top US hope John Isner in four tight sets.
"I've played quite a few times with Rafa. When you play these top guys you have to come up with your great tennis," said Cilic, who has won just twice in eight tries against Nadal.
Sixth seed Zverev, coming off back-to-back five-set matches, made it to the second week in New York for the first time after fighting past Aljaz Bedene 6-7, 7-6, 6-3, 7-6 in three hours and 36 minutes.
Nick Kyrgios' eventful US Open ended in the third round as Russian Andrey Rublev turned aside the Australian 7-6, 7-6, 6-3 in a battle of big servers.
Rublev looked up to the task from the start and proved to be unflappable against Kyrgios, who complained to his team in the box several times about not being able to see and later said he took time adjusting to the massive Arthur Ashe Stadium.
The Australian seemed to have no issues with his vision on serve, however, at one point firing four consecutive aces in a 40-second game to force a first-set tiebreak.
Kyrgios got his only two break point chances while leading 3-2 in the second set but Rublev beat them both back.
The pair remained on serve to bring up another tiebreak and while Kyrgios jumped out to a 4-0 lead a determined Rublev took seven of the next eight points to snatch the set and grab control of the match.
"I had chances. I just didn't take them," said Kyrgios. "Nowhere near my best tennis, but it is what it is."
Canadian teenager Bianca Andreescu, seeded 15th, brushed past two-time US Open runner-up Caroline Wozniacki 6-4, 6-4 to extend her best grand slam run.
The 19-year-old, a winner at Toronto and Indian Wells this season, improved to 30-4 for the year despite missing much of the clay and grass portion with a shoulder injury.
"I think everything is just clicking with me," said Andreescu, who had never gone beyond round two at a major prior to this tournament.
"I've been through a lot with injuries and have just taken everything I've learned from the past couple of years and brought it into this year."
American qualifier Taylor Townsend vowed to ride her surprise US Open run "all the way" after reaching the last 16 for the first time at a slam.
Townsend, ranked 116th, followed up her shock win over reigning Wimbledon champion Simona Halep by beating another Romanian, Sorana Cirstea, 7-5, 6-2.
"I didn't know that many people had my phone number," Townsend said when asked how she coped in the wake of her Halep upset.
"I got a lot of messages. It was a lot of love. My phone started dialing 911 by itself, I don't know what that was about. I just tried to keep my head on straight.
"I'm going to take it as far as I can. We're going to ride this thing all the way."
Swiss 13th seed Belinda Bencic advanced via walkover as Anett Kontaveit retired with illness, while Belgian 25th seed Elise Mertens moved on with a 6-3, 6-3 defeat of Germany's Andrea Petkovic.
US wildcard Kristie Ahn, winless in three previous Slam appearances, kept her fairytale run going by knocking out 2017 Roland Garros winner Jelena Ostapenko.