The British number two has made no secret of the fact he does not like playing Nishioka, who is known for his speed around the court and retrieval skills, and he was unable to end his losing run despite being ranked 31 places higher.
Evans had already lost to the Japanese player twice this year, in Miami and Washington, and he made the worst possible start by dropping serve in the first game.
Evans twice broke Nishioka when he served for the match in the second set, saving a match point at 5-6, but was unable to come out on top in the tie-break, losing out 6-2 7-6 (3).
Elsewhere, Jenson Brooksby showed great resolve in his victory over qualifier Wu Tung-Lin.
The American, who is seeded eighth in Seoul, sealed a 7-6, 3-6, 6-0 victory in the first-round of the ATP 250 event.
Wu showed a lot of fight in the two-and-a-half hour battle, though he ultimately succumbed to the quality of Brooksby.
Mackenzie McDonald and Steve Johnson both progressed with straight sets victories, while world number 82 set up a clash with third seed Taylor Fritz.
Nicolas Jarry, on the other hand, will be Casper Ruud's second-round opponent after getting the better of lucky loser Ryan Peniston.
The Brit was unable to join Evans in the winner's circle after falling to a 6-3 7-6 defeat against the Chilean qualifier.