It's a very simple thing: I like what I do. I like playing tennis. I know it's not forever. I like to feel myself competitive. I like to fight for the things that I have been fighting for almost half of my life or even more. And that's it. It's not that complicated to understand.

— Rafael Nadal, when asked why he kept going despite recurring injuries

Defending champion Rafael Nadal hobbled out of the second round in a huge upset at the Australian Open on Wednesday, as Coco Gauff beat Emma Raducanu in a battle of the rising stars.

Nadal's wife Mery was in tears as the injury-hampered Spanish great lost to 65th-ranked Mackenzie McDonald at Rod Laver Arena, where the roof was closed because of more rain in Melbourne.

The 36-year-old Nadal was clearly hindered by a hip issue that required a medical timeout, as he surrendered 6-4, 6-4, 7-5 to the American.

It was the reigning champion's earliest exit from a major in seven years and will lead to more questions about whether injury and age are catching up with the record 22-time major champion.

The men's title now looks Novak Djokovic's to lose.

Nadal said defeat "hurt" and acknowledged that injuries were taking a toll.

"Sometimes it's frustrating. Sometimes it's difficult to accept. Sometimes you feel super tired about all this stuff in terms of injuries. I can't come here and lie and say that the life is fantastic. Not now. Tomorrow starts another day," Nadal said. "Now it's a tough moment. It's a tough day, and you need to accept that, and keep going.

"I've never been in a position to complain, life has given me so many positive things that I have no right to complain," he said. But I am tired, I am sad, I am disappointed, all this is a reality. From here on... what I want is to continue playing tennis. Don't think I'm saying all this because I want to take a step back. It is not the case, but my current feelings are bad."

In contrast to Nadal's disappointment and pain, 27-year-old McDonald is into the third round and a match against Yoshihito Nishioka of Japan.

"He's an incredible champion, he's never going to give up regardless of the situation," said McDonald of his beaten opponent. "I was trying to stay focused on what I was trying to do and he kind of got me out of my rhythm, and I just got through it."

With McDonald leading 6-4, 5-3, Nadal left the court with a physio for a medical timeout, and it was unclear if he would return. But the Spaniard showed his trademark fighting spirit by continuing on. Ultimately, the deficit and injury were too much to overcome.

 "I was not able to hit the backhand at all. I was not able to run for the ball. But I just wanted to finish the match," Nadal said.

In the women's draw, 18-year-old American Gauff, seen as the heir to now-retired Serena Williams, defeated Britain's Raducanu 6-3, 7-6 (7/4). There are 70 places separating seventh seed Gauff and 2021 US Open champion Raducanu in the rankings, but you wouldn't have known it as the pair tussled for an hour and 42 minutes of pulsating tennis on Rod Laver Arena.

It was a first-ever meeting between the two and a glimpse of an exciting future for women's tennis.

Earlier, world number one Iga Swiatek and dangerous American Jessica Pegula led the charge into the third round.