And he did so in typical style, rallying from an early deficit to down home hope John Isner 4-6, 6-4, 6-4 in the Citi Open final.
Isner snatched the opener with a pair of screaming forehand returns in the 10th game, earning the first break of the match.
Nishikori fought back, opening the second set with an immediate break and consolidating to love for 2-0. Isner received treatment on his right shoulder after the third game and the Japanese refused to relinquish his advantage, sending the final encounter to a one-set sprint.
In the third, #Nishikori did not let his foot off the gas, grabbing a break in the third game and holding serve to the finish line.
The World No. 5 has been a dominant force in deciding sets, now owning a 13-3 record this year when going the distance. He has won 34 of his last 40 such matches. Nishikori, who was appearing in his 15th ATP World Tour final, captured his 10th title.
Three of the Japanese’s last four titles have come at the ATP World Tour 500 level, winning on the clay of Barcelona this year after hoisting the trophy on home soil last October in Tokyo. Nishikori earns $343,000 and 500 Emirates ATP Rankings points.
American Sloane Stephens won the female category, beating Anastasia Pavlyuchenkov, 6-1, 6-2.
It was the first WTA title of her career.
Stephens had never reached a WTA final – in fact the World No.35 was the only player in the Top 40 never to achieve the feat. But she finally shook that tag with a semifinal win over the No.2 seed, Samantha Stosur, and then cruised past Pavlyuchenkova in her first final, 6-1, 6-2.
A former World No.11, Stephens will now move back into the Top 30 on the new WTA Rankings.