World number three Stefanos Tsitsipas faced audible jeers from the US Open crowds during his second-round win against Adrian Mannarino on Wednesday.
The Greek hit a career-high 27 aces during his 6-3 6-4 6-7 (4-7) 6-0 win, but was once again criticised for a lengthy mid-match toilet break.
Former champion Andy Murray raised the issue during the previous round.
But fans on Arthur Ashe Stadium were once again made to wait over eight minutes for the player.
During the delay, his opponent was forced to ask for some balls to hit in order to stay loose, and upon his return, Tsitsipas was met by a chorus of boos from the crowd at Flushing Meadows.
The jibes did not affect his performance as he powered through the final set to love, setting up a third-round tie with Spanish teenager Carlos Alcaraz.
When asked about his lengthy pause in play, the 23-year-old said he was completely soaked with sweat after the third set and wanted ‘to feel refreshed’.
Stormy conditions had earlier interrupted play between Argentine 11th seed Diego Schwartzman and South African Kevin Anderson.
Rainwater had managed to find its way on to the court, despite the roof of Louis Armstrong Stadium being closed, with fans having to use umbrellas.
Once play was back under way on the more sheltered Ashe court, Schwartzman took the win 7-6 (7-4) 6-3 6-4.
He will face Slovakian Alex Molcan in the third round.
Earlier in the day, world number two Daniil Medvedev sailed through to the third round with a comfortable 6-4 6-1 6-2 victory over Dominik Koepfer.
Medvedev was broken once by the German in the first set but immediately responded and led throughout.
The Russian second seed hit eight aces and won 80% of points on his first serve in a commanding performance under the roof on Arthur Ashe Stadium.
He faces Spaniard Pablo Andujar in the third round.
Meanwhile, Russian fifth seed Andrey Rublev beat Spaniard Pedro Martinez 7-6 (7-2) 6-7 (5-7) 6-1 6-1 to set up a third-round meeting with American Frances Tiafoe.
In front of a noisy home crowd on Louis Armstrong Stadium, 23-year-old Tiafoe played superbly to win 6-1 6-2 7-5 against Argentina's Guido Pella and set up a first senior meeting with Rublev.
Canadian 12th seed Felix Auger-Aliassime advanced with a 7-6 (7-5) 6-3 6-2 win over Spain's Bernabe Zapata Miralles.
Spanish teenager Alcaraz again demonstrated why he is one of the sport's most-talked about young stars by beating France's Arthur Rinderknech in four sets.
