Anderson, who also won in New York in February and reached the final at Wimbledon, earned a fifth career title but first at a higher-level ATP 500 event. He became the sixth player to qualify for the eight-man, season-ending event in London, joining Rafael Nadal, Novak Djokovic, Juan Martin del Potro, Roger Federer, and Alexander Zverev.
A winner of 11 events, Nishikori hasn't triumphed since winning in Memphis in February 2016. But reaching Sunday's final, his third of the season, boosted the fifth-seeded Japanese's chances of also advancing to the ATP finals.
Anderson's strong serve was a decisive factor. The second-seeded South African won 91 percent of points on his first serve, and his 13 aces raised his total for the week to 69. In the fourth game of the opening set, Anderson used his sixth break point to go 3-1 up, the only time in the match a player lost his serve.
Anderson missed the only chance of another break at 4-4 in the second set, but quickly took a 3-0 lead in the tiebreaker before closing out the win on his first match point. Nishikori still leads Anderson 4-3 in their head-to-head statistics, though he lost both of their matches this year.
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