Shapovalov surges into final of Korea Open
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Shapovalov defeated eighth seed Jenson Brooksby of the United States 7-5, 6-4 on Saturday while Nishioka beat another American, Aleksandar Kovacevic, 6-3, 4-6, 6-3 in the other semi-final in Seoul.
"Brooksby was definitely a tough opponent," said Shapovalov, who rose to a career-high 10th in the world two years ago but is now ranked 24.
"But I prepared for the match well and I had some practice time with him, which helped."
The 23-year-old Shapovalov's only previous ATP title came in Stockholm in 2019.
Shapovalov and Nishioka have faced each other once before, with the 56th-ranked Japanese winning in the round of 16 at the 2018 Shenzhen Open.
Nishioka stunned world number two Casper Ruud of Norway in the quarter-finals.