What appeared at the outset to be a routine match for the seventh-seeded Japanese turned into a surprise challenge from American Klahn.
After a tepid start, Klahn won all his first serve points in the second set and saved three of the four break point opportunities against him.
Nishikori, who reached the semi-finals last year and in 2016, broke Klahn to take the third set, switching the momentum back in his favour and dominating the longer rallies.
Inconsistency ultimately proved Klahn’s downfall as the 29-year-old committed 62 unforced errors in the match, 30 more than his opponent.
“(In the) second and fourth sets… I didn’t play aggressive as like the first or third sets. That cost me a set,” said Nishikori.
“He served pretty fast and accurate, too. And also (his) second serve, he hits big. I think he has a great serve for his height. He’s not the biggest guy on the tour. But I think he has great serve.”
Nishikori, who had rued his lack of playing time after his first-round opponent was forced to retire, was joined by his usual crowd of excitable fans, shielded from the soggy conditions under Louis Armstrong’s retractable roof.
He will face either 31st-seeded Cristian Garin of Chile or Australia’s Alex de Minaur in the third round. (Reuters/)
Edited by Maharazu Ahmed