Fifth seed Andrey Rublev claimed a straight-set victory against 42-year-old qualifier Ivo Karlovic to reach the US Open second round.
The 23-year-old Russian beat the Croat - the oldest US Open qualifier in the Open era - 6-3 7-6 (7-3) 6-3.
Karlovic's compatriot Marin Cilic also exited the tournament, with the 2014 champion retiring from a match for the first time in his 837-match career.
As a result, Germany's Philipp Kohlschreiber advanced.
Rublev will play Spain's Pedro Martinez next, while Kohlshreiber will face Spaniard Pablo Andujar.
South African Kevin Anderson equalled his career best tally of aces by firing 49 past Jiri Vesely to wrap up a 7-6 (7-1) 4-6 3-6 7-6 (7-5) 7-6 (7-4) victory in four hours and 22 minutes.
The 2017 runner-up will face Argentine 11th seed Diego Schwartzman in the second round, with Norwegian eighth seed Casper Ruud and Canadian 12th seed Felix Auger-Aliassime also progressing.
Serbian top seed Novak Djokovic begins his bid to win a men's record 21st Grand Slam title on Tuesday, while Roger Federer and Rafael Nadal are absent through injury.
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