Tiafoe hit 17 aces and won a three-setter for the fourth time this month.
No. 8 Chung Hyeon became the highest-seeded player to reach the quarterfinals when he eliminated Franko Skugor 6-4, 7-6 (4). Denis Shapovalov, an 18-year-old Canadian, beat American Jared Donaldson 6-7 (6), 6-4, 6-4.
Copyright 2018 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.