Kei Nishikori's run at the Acapulco Open came to an early second-round end on Wednesday as American Sam Querrey beat the world No. 6, 6-4, 6-3 to advance.
Nishikori entered the match having recently beaten Querrey twice, once in straight sets at the Japan Open in late 2015 and then on the way to the title at his most recent tournament in Memphis.
In Acapulco, however, Nishikori was thoroughly outplayed, dropping his serve three times in the straight-sets loss as Querrey, ranked 43rd in the world, beat Nishikori for the first time since 2012.
Querrey attacked the second seed's serve relentlessly, but Nishikori did not do himself any favors by only getting a pitiful 46 percent of his first serves in play.
"I had no chance with returning his serve and it wasn't my day," Nishikori said. "Both of us were making mistakes and that made it even harder to find a rhythm.
"My opponent played well but my serves weren't getting in at all, and 90 percent of the reason for the defeat is with me. My second serves, too, were right down the middle and he was attacking me off of them."
Next up for Querrey is 18-year-old American compatriot Taylor Fritz, who Nishikori beat in the Memphis final.
In the women's draw, 18-year-old Naomi Osaka won her second-round match, beating Mariana Duque-Marino of Colombia 6-3, 7-6 (7-5).
In the quarterfinals, Osaka will face second seed Sloane Stephens of the United States. Stephens beat Olga Govortsova 6-4, 6-1.