Stefanos Tsitsipas suffered an early US Open exit for the seventh year in a row as the 11th seed lost to Thanasi Kokkinakis in the first round.
Greek Tsitsipas has never gone beyond the third round in New York, losing in the first round on three occasions.
He struggled for consistency once again in a 7-6 (7-5) 4-6 6-3 7-5 loss to Australian world number 86 Kokkinakis.
Tsitsipas is the highest-ranked player to lose on the men’s side of the draw in the first two days at Flushing Meadows.
A two-time Grand Slam finalist, Tsitsipas has had a mixed year, with his best major showing a quarter-final appearance at the French Open.
He halted his coaching partnership with his father in the lead-up to the US Open, having being critical of his coaching tactics in his recent Cincinnati Open exit.
But Tsitsipas had his chances against Kokkinakis – he was 40-0 up on serve at 3-4 down in the third set before being broken and was broken cheaply at 5-5 in the fourth.
Tsitsipas converted just three of his 10 break point opportunities, compared to four out of eight by Kokkinakis in the near four-hour match.
Kokkinakis, who had only reached the second round once in five previous attempts in New York, will play either Nuno Borges of Portugal or Argentina’s Federico Coria next.