Nick Kyrgios ended Daniil Medvedev's defence of the US Open title as he earned an enthralling four-set win on an entertaining night in New York.
The 27-year-old Australian demonstrated all of his shot-making - and propensity for creating drama - in a 7-6 (13-11) 3-6 6-3 6-2 win in the last 16.
Medvedev will lose his ranking as world number one after the defeat.
Wimbledon runner-up Kyrgios goes on to play another Russian, 27th seed Karen Khachanov, in the quarter-finals.
Khachanov reached his third Grand Slam quarter-final by outlasting Spanish 12th seed Pablo Carreno Busta in a 4-6 6-3 6-1 4-6 6-3 win.