Novak Djokovic slumped to his earliest exit at the us open in 18 years when he lost 6-4, 6-4, 2-6, 6-4 in the third round to Australia’s 28th-ranked Alexei Popyrin.

Defeat for the 37-year-old Djokovic, a four-time champion in New York, left him frustratingly short once again of winning a record 25th Grand Slam Title.

Alexei Popyrin insisted that his shock us open triumph over defending Champion Novak Djokovic was not unbelievable and that winning his maiden masters title in Montreal on the eve of the tournament was way bigger".

The victory also condemned former world number one Djokovic to his earliest exit in New York since 2006 when he fell to another Australian, Lleyton Hewitt.

Popyrin had lost all three of his previous meetings with Djokovic, including at this year's Australian Open and Wimbledon.