Mackenzie McDonald earned the biggest win of his career at the Australian Open after beating the defending champion Rafael Nadal in the second round at Rod Laver Arena.

The American got the better of the ailing Spaniard 6-4, 6-4, 7-5 as his lean start to the tennis season continued with another early loss.

Nadal has not looked in peak shape this year as last year’s injuries have taken their toll on the 36-year-old. He also struggled in the first-round match but managed to eke into the second round.

But McDonald refused to stand back and let Nadal impose his will, breaking the lefty in the first game to signal what was to come. He would go on to break him a total of five times during the two hours and 32-minute contest.

At 4-3 in the second set, Nadal moved to his left to chase a forehand on the first point of the game when he pulled up in pain with an apparent upper left leg injury. At 5-3, the defending champion left the court with a physio for a medical timeout.

With the 23-time major winning never looking the same, Mackenzie McDonald grabbed the golden opportunity with both hands to complete a memorable upset.

It was the earliest exit for Nadal since he lost in the first round of the 2016 Australian Open in five sets against countryman Fernando Verdasco.

With the no1 seed gone, Novak Djokovic becomes an immediate favourite to win his 10th Australian Open title.