Seven-time champion and third seed Roger Federer was knocked out of the Cincinnati Masters by world number 70 Andrey Rublev in the third round on Thursday.
Rublev won 6-3, 6-4 and will face fellow Russian Daniil Medvedev, the ninth seed, for a place in the semi-finals.
Federer, 38, will now head into the US Open later this month with just two matches on hard courts under his belt.
Cincinnati was his first tournament since losing the Wimbledon final in July to Novak Djokovic.
Rublev, 21, took less than an hour to earn his second top-five win in a month after beating Dominic Thiem in Hamburg on his way to the final. Rublev shed tears of joy after pulling off the biggest win of his career.