Novak Djokovic flags Alexei Popyrin as potential US Open champ after upset third round win

Novak Djokovic has hailed Alexei Popyrin as a legitimate US Open title contender after the audacious Australian rocked the Serbian superstar’s grand slam dreams in New York.

Djokovic rued “some of the worst tennis I have ever played” after coughing up 14 double-faults in his 6-4, 6-4, 2-6, 6-4…