Australian Open 2018: Grigor Dimitrov digs deep to avoid shock defeat

Dimitrov only hit five winners on his backhand

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 form has made him one of the favourites for the title, eventually came through 4-6 6-2 6-4 0-6 8-6 after three hours and 25 minutes.

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

But the 26-year-old held his nerve to seal victory in a tense final set.

"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.

"I'm so happy with the result and the fight."

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).

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McDonald only recorded his first Tour-level victory in the first round but was not daunted by playing on a packed Rod Laver Arena in the first match of the night session.

His powerful serve and aggressive tactics restricted Dimitrov to only seven winners on his way to taking the first set.

The Bulgarian, who won the season-ending ATP Finals in London, seemed to have regained control in the second and third sets but McDonald came back in spectacular fashion to take the match to a decider.

Dimitrov double faulted three times in the final set but kept his composure under the lights, and finally the American double-faulted to give him match point.

McDonald hit a forehand into the net to ensure Dimitrov's place in the third round and a clash with Russian 30th seed Andrey Rublev.

Nadal heads indoors to avoid the heat

Rafael Nadal has come through two straight-set matches in Melbourne so far

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

"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.

With temperatures in Melbourne set to rise to 40C on Thursday and Friday, Nadal said he wants tournament organisers to consider shutting the roofs on the show courts that have them.

"I think it's a health issue," said the Spaniard. "Even though I like sometimes to play with heat. When it's too much, it becomes dangerous for the health.

"I would not like to see here retirements, conditions that create a bad show for the crowd.

"The crowd is suffering too. In the courts that we have the roof, why not put the roof when the conditions are so extreme? I'm going to practise indoors tomorrow."