Third seed Grigor Dimitrov was pushed to the limit before scraping past American qualifier Mackenzie McDonald in the Australian Open second round.

The Bulgarian, whose recent form has made him one of the favourites for the title, eventually came through 4-6 6-2 6-4 0-6 8-6.

Dimitrov struggled from the start as world number 186 McDonald played the match of his career.

But he fought back to win in three hours and 25 minutes.

“He deserves a lot of credit. He played an unbelievable game,” said Dimitrov. “I had to fight so much and in the end I think my experience helped me.”

McDonald only recorded his first Tour-level victory in the first round.

Top seed Rafael Nadal earlier progressed to the last 32 with a straight-set victory over Argentina’s Leonardo Mayer.

The Spaniard, 31, beat world number 52 Mayer 6-3 6-4 7-6 (7-4) in two hours 38 minutes on Rod Laver Arena.

Mayer responded to a Nadal break in the final set with one of his own, before the 2009 champion took the tie-break.

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“I’m happy to be in the third round and a second victory in a row is very important news for me,” said Nadal.

“Leonardo is a player with big potential, he hits the ball so strong. He is a very dangerous opponent.

“This tournament is my favourite of the year, so I want to stay here as long as possible.”

Nadal will face Bosnia and Herzegovina’s Damir Dzumhur in the next round after the world number 30 beat John Millman 7-5 3-6 6-4 6-1.