New York - 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.
US Open results on Monday (x denotes seeding):
Men
1st round
Denis Kudla (USA) bt Janko Tipsarevic (SRB) 3-6, 6-1, 7-6 (7/5), 6-1
Dusan Lajovic (SRB x27) bt Steve Darcis (BEL) 7-5, 6-3, 6-3
Jenson Brooksby (USA) bt Tomas Berdych (CZE) 6-1, 2-6, 6-4, 6-4
Bradley Klahn (USA) bt Thiago Monteiro (BRA) 6-3, 6-2, 6-3
Kei Nishikori (JPN x7) bt Marco Trungelliti (ARG) 6-1, 4-1 retired
Women
1st round
Rebecca Peterson (SWE) bt Monica Puig (PUR) 6-3, 6-3
Johanna Konta (GBR x16) bt Daria Kasatkina (RUS) 6-1, 4-6, 6-2
Margarita Gasparyan (RUS) bt Priscilla Hon (AUS) 7-6 (7/4), 6-4
Ekaterina Alexandrova (RUS) bt Samantha Stosur (AUS) 6-1, 6-3
Ons Jabeur (TUN) bt Caroline Garcia (FRA x27) 7-6 (10/8), 6-2
Mariam Bolkvadze (GEO) bt Bernarda Pera (USA) 6-3, 5-7, 6-4
Karolina Pliskova (CZE x3) bt Tereza Martincova (CZE) 7-6 (8/6), 7-6 (7/3)
Petra Martic (CRO x22) bt Tamara Zidansek (SLO) 6-4, 4-6, 6-1
Ana Bogdan (ROM) bt Harriet Dart (GBR) 6-3, 6-1
Anastasija Sevastova (LAT x12) bt Eugenie Bouchard (CAN) 6-3, 6-3
Ashleigh Barty (AUS x2) bt Zarina Diyas (KAZ) 1-6, 6-3, 6-2