Nick Kyrgios ended Daniil Medvedev's defence of the US Open title as he earned a thrilling 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, 26, 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.
Kyrgios has regularly demonstrated over the years he has the talent to win one of the major tournaments, but said he had been in some "really scary places mentally" which had stopped his progress.
Reaching the Wimbledon final, where he lost to Novak Djokovic, showed he had figured out what he needed to do on and off court to be successful.
His form has been transferred to the North American hard courts - winning the Washington title and now going further at Flushing Meadows than before.
