New York, USA: Former US Open runner-up Kei Nishikori of Japan raced into the second round in just 47 minutes on Monday after Argentine qualifier Marco Trungelliti quit with injury.
Seventh seed Nishikori led 6-1, 4-1 when world number 205 Trungelliti was forced to retire due to a back problem.
Nishikori will meet either Thiago Monteiro of Brazil or American Bradley Klahn in the next round.
The Japanese star, a 2014 finalist in New York, has reached the quarter-finals or better in his last five Grand Slam appearances.
In the women's event, Czech third seed Karolina Pliskova overcame compatriot and qualifier Tereza Martincova in two tie-breaks in her opening match.
Pliskova, the 2016 runner-up at Flushing Meadows, advanced 7-6 (8/6), 7-6 (7/3) to set up a second-round meeting with American Bernarda Pera or Georgian qualifier Mariam Bolkvadze.