Qualifier Dustin Brown, who hadn't won an ATP Tour match since 2017 before this week, stunned top-seeded Alexander Zverev 6-4, 6-7 (3), 6-3 in a second-round matchup of German players in the MercedesCup at Stuttgart, Germany.
Brown, ranked 170th in the world, beat a top-10 player for the fifth time in his career. He was slowed over the past two years by a back injury.
Zverev wasn't the day's only upset victim. Second-seeded Karen Khachanov of Russia fell 6-4, 6-2 to Italy's Matteo Berrettini, and fifth-seeded Gael Monfils of France lost 7-5, 6-7 (3), 7-6 (3) to the United States' Denis Kudla.
Also advancing to the quarterfinals was seventh-seeded Canadian Felix Auger-Aliassime, who beat France's Gilles Simon 7-5, 6-4.
Chile's Nicolas Jarry advanced to the quarterfinals with a 6-4, 3-6, 6-4 upset of top-seeded Stefanos Tsitsipas of Greece in 's-Hertogenbosch, Netherlands. Jarry saved five of the six break points he faced, and he converted two of his four break chances.
Fourth-seeded Fernando Verdasco of Spain also fell 1-6, 6-3, 6-4 to France's Adrian Mannarino.
In other second-round matches, fifth-seeded David Goffin of Belgium beat France's Pierre-Hugues Hebert 6-3, 7-5, and seventh-seeded Cristian Garin of Chile topped the Netherlands' Robin Haase 7-5, 7-5.
--Field Level Media