MELBOURNE, Jan. 18 (Xinhua) -- Defending champion and top seed Rafael Nadal crashed out of the Australian Open on Wednesday after going down 6-4, 6-4, 7-5 to unseeded Mackenzie McDonald of the United States in the second round.

Spain's Rafael Nadal leaves the court after losing to USA's Mackenzie McDonald in their men's singles match on day three of the Australian Open tennis tournament in Melbourne on January 18, 2023. (Photo: AFP)

Nadal lost his first two service games, with world No. 65 McDonald taking a 4-1 lead before claiming the set 6-4.

When the 27-year-old McDonald charged into a 5-3 lead in the second set, a physio examined Nadal's left thigh. The top seed later went off court for a medical timeout. Though Nadal returned and clawed one game back, McDonald seized his chances to take the set.

Tensions kept mounting in the third set, as both players won their service games and leveled the score at 5-5. McDonald broke for a narrow 6-5 lead and sealed his straight-set triumph over Nadal by holding his serve in the final game.

McDonald fired 14 aces throughout the match, while Nadal only landed six, all of which came in the third set.

After the match, Nadal said he suffered a hip injury in the second set, adding that the pain had been present for a couple of days, "but nothing like today in that movement."

"I have a history in the hip that I had issues. I had to do treatments in the past, [but it] was not this amount of problem. Now I feel I cannot move," he noted.

Speaking of his disappointment at the result, the 22-time Grand Slam winner said it was difficult for him.

"I can't say that I am not destroyed mentally at this time, because I will be lying," said Nadal. "I went through this process too many times in my career, and I am ready to keep doing it."

Nadal and McDonald had one head-to-head previously - in the second round of the French Open last year, with the Spaniard emerging victorious 6-1, 6-3, 6-3.

USA's Mackenzie McDonald hits a return against Spain's Rafael Nadal during their men's singles match on day three of the Australian Open tennis tournament in Melbourne on January 18, 2023. (Photo: AFP)

The last time Nadal bowed out of a Grand Slam at such an early stage was at the 2016 Australian Open, where he suffered a narrow 7-6 (6), 4-6, 3-6, 7-6 (4), 6-2 loss to his compatriot Fernando Verdasco in the opening round.

"He didn't even want to roll over and quit. He kept fighting until basically the end, even though he maybe didn't have all his game," McDonald told reporters of his match with Nadal.

"But I would say once I broke him maybe in that third set at the end there, it felt like he hadn't really seen any chances on my serve in that set, so I think I could have gone away with it there," he added.