Alexander Zverev and Stefanos Tsitsipas joined Novak Djokovic in advancing at the US Open on Monday.
Zverev and Tsitsipas, two players capable of threatening Djokovic in New York, posted strong first-round wins at Flushing Meadows.
Djokovic, the world number one, cruised through on what was a good day for the seeds.
Of the 16 men's seeds in action, 13 advanced.
ZVEREV, TSITSIPAS GET THE JOB DONE
Zverev, a semi-finalist at the Australian Open this year, needed more than three hours to get past Kevin Anderson 7-6 (7-2) 5-7 6-3 7-5.
The 2017 US Open finalist, Anderson was unable to take his chances, converting just two of five break points as Zverev capitalised on three of his four.
Zverev has never been beyond the fourth round at the US Open, but the German fifth seed could challenge this year.
Awaiting Zverev in the second round is Brandon Nakashima, who beat Paolo Lorenzi in his opener.
Tsitsipas matched his best result at the US Open by reaching the second round with a 6-2 6-1 6-1 thrashing of Albert Ramos-Vinolas.
The Greek fourth seed dominated Spain's Ramos-Vinolas, losing just 18 points on serve and not facing a break point.
DJOKOVIC CONTINUES FINE FORM
Djokovic continued his good form, easing past Damir Dzumhur 6-1 6-4 6-1.
After improving to 23-0 this year by winning the Western & Southern Open, Djokovic showed few signs of fatigue despite a second-set battle.
Djokovic maintained his record of having never lost in the first round at the US Open, improving that record to 15-0.
The world number one is set to face a tougher battle in the second round, where Brit Kyle Edmund awaits.
Edmund was too good for Alexander Bublik 2-6 7-5 7-5 6-0, but has lost five of his six meetings with Djokovic.
Of the 16 seeds in action, 13 advanced to the second round.
David Goffin (seven), Denis Shapovalov (12), Cristian Garin (13), Taylor Fritz (19), Pablo Carreno Busta (20), Hubert Hurkacz (24), Filip Krajinovic (26), Borna Coric (27), Jan-Lennard Struff (28) and Adrian Mannarino (32) all advanced.
The three seeds to fall were Diego Schwartzman (nine), John Isner (16) and Dusan Lajovic (18).
Isner played almost four hours before going down to Steve Johnson 6-7 (5-7) 6-3 6-7 (5-7) 6-3 7-6 (7-3) in a thriller.
Schwartzman fell to Cameron Norrie in five sets, while Lajovic was edged by Egor Gerasimov.