Reigning Australian Open champ Rafael Nadal loses to Mackenzie McDonald after picking up mid-match hip injury 

Top men's seed Rafael Nadal saw his Australian Open title defense come crashing down Wednesday, with a mid-match injury hampering the 22-time major champion in an eventual 6-4, 6-4, 7-5 second-round defeat to Mackenzie McDonald.

After the 27-year-old American regained his break advantage for 4-3 in set two, Nadal pulled up gingerly in the next game when moving to his forehand side in the ad court on Rod Laver Arena. He barely reacted to McDonald’s last two serves as the former NCAA champion consolidated, before calling for the trainer.

With pain appearing to stem from his left hip, the 36-year-old left for an off-court medical timeout. Upon returning, he valiantly held, though was visibly compromised. Wife Mery was spotted crying in the stands.

"Is difficult to make resolution if it's a muscle, if it's the joint, if it's the cartilage. I don't know," Nadal said in press afterwards.

Nadal mulled over the situation during the set break and opted to play on with a go-for-broke strategy. His first two aces of the match enabled the left-hander to get on the scoreboard first. He tried shortening points with serve-and-volley looks and big forehand cuts up the line as the third set wore on.

"I consider all the time stopping, but I didn't ask the physiotherapist at the end. I have to know myself," stated Nadal. "And I tried to keep playing without increasing the damage. No, that's it. 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. That's it."

Assessed McDonald afterwards, "I don't know what the stats were, but felt like he had more aces and actually hit more winners in the third set because he was going for it. But then again, he was behind a little bit with the running. So it made me think, 'Do I go for it too, or do I just make more balls?' I definitely hesitated a bit."

Another timely ace off Nadal’s racquet wiped away a break point in the ninth game, but McDonald broke through the next time around—and subsequently served it out at 15. This marks Nadal's earliest exit at a major since being ousted by countryman Fernando Verdasco in the first round at Melbourne Park seven years earlier.

"It's a very simple thing: I like what I do. I like playing tennis. I know it's not forever," said Nadal. "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.

"When you do things that you like to do, at the end of the day, it's not a sacrifice."

McDonald had compiled an impressive display on his end of the court by taking away time from Nadal until the Spaniard came up hurt. He finished with 14 aces, compiling 42 winners to 22 unforced errors.

"I'm very happy with how I competed in the first couple of sets and executed the game plan," reflected McDonald. "I feel like I'm working really well with my coach, Robby (Ginepri), and he gave me a good game plan. I stuck to it and stuck with my guns and didn't kind of go in [with] any fear or anything."

The world No. 65 advances to face the winner of No. 31 seed Yoshihito Nishioka and qualifier Dalibor Svrcina. A win would see McDonald equal his round-of-16 showing here two years ago, his best major performance.

We’ll continue to update this developing story.