Nishikori outfought Robert Kendrick, 7-6 (7-3), 6-7 (5-7), 6-2. Neither player faced a break point until the third set. Nishikori was able to save both break points he faced and broke Kendrick's serve twice in the decisive set to win the match.
While Kendrick fell, three other Americans advanced to the tournament's second round. Jesse Levine took out Danai Udomchoke, 4-6, 6-1, 6-0; Bobby Reynolds defeated Tatsuma Ito, 6-3, 6-1, and Wayne Odesnik topped Kevin Kim, 6-4, 6-3.
Other winners Tuesday were Dudi Sela, Cecil Mamiit, Martin Slanar, Flavio Cipolla, Joseph Sirianni, Simon Stadler, Roko Karanusic and Yen-Hsun Lu.
The top 16 seeds, including No. 1-seeded and defending Japan Open champion David Ferrer, received first-round byes and have their first court action Wednesday.