Rafael Nadal was relieved to have survived a "big battle" with Alexander Zverev at the Australian Open.

Former world number one Nadal trailed two sets to one but fought back to secure a 4-6 6-3 6-7 (5-7) 6-3 6-2 victory over Zverev in a match lasting four hours and five minutes.

The Spaniard felt his mental strength against an opponent he rates highly helped guide him into the fourth round.

"You cannot pretend to be in the fourth round of the Australian Open and have an easy opponent. Every match is so difficult. This was a big battle, I'm very happy to be through," he said in an on-court interview.

"I lost the last couple of times in the fifth set so I said to myself 'today is the day'. With this crowd everything is less difficult.

"I think people know how good Alexander is. As I said the other night he's the future of our sport and the present too. It was a very tough match for me.

"I didn't start playing my best, he was trying to push me back and I was not feeling very good as I was losing too much court and he was able to take the advantage from inside.

"Then I changed the dynamic and in the third [set] I was feeling better, I had more time to control the point from the baseline, but his serve was huge.

"In the tie-break it was a close one [but] he deserved it, he was more aggressive than me and after that I said to myself to fight for every point, forget about the result and that's what I tried."