Reigning US Open champion Emma Raducanu crashed out of the Australian Open in the second round Thursday as she struggled with blisters on her hand so bad that some of her team had urged her not to play.

The 19-year-old, making her debut at Melbourne Park, looked on track when she raced to a 3-0 lead in the opening set against Montenegro's Danka Kovinic.

But the 17th seed then lost five games in a row and needed a medical timeout for treatment on her right, racquet hand, and said afterwards that the blisters were so bad she had only been able to practise backhands.

Despite battling back she couldn't stop 98th-ranked Kovinic winning 6-4, 4-6, 6-3 on Margaret Court Arena.

"I was struggling with my hand before the match. There were some people in my team that maybe didn't want me to play, but I wanted to go out there and fight through it, see how far I could get," said the Briton.

"I thought it was a pretty good learning experience for me. I discovered tools about myself and my game that I didn't know I had before.

"I can take some positives even from this match."

Raducanu added that she had suffered from blisters before on her hand "but never this bad".

"I actually wasn't hitting forehands in practice the last few days. I was only saving it for my match. I wasn't hitting serves, either.

"So the only thing I was really practising was my backhand," she said.

The result put Kovinic into the third round of a major for the first time.

She will now play two-time Grand Slam winner Simona Halep, seeded 14, who crushed Brazilian Beatriz Haddad Maia 6-2, 6-0 for a place in the fourth round.

"It's my first time to be in the third round after so many years and it is, honestly, an amazing feeling because I really wanted this for so long," said Kovinic, 27.

"And I'm so glad that I can be the first Montenegrin ever to make it to this  round. I'm making these results and making history in tennis for Montenegro. It's a huge thing for me."

Raducanu applied pressure on the Kovinic serve right away, working a break point that went in her favour. A comfortable hold followed then Kovinic's sixth unforced error handed the teenager three break points to go 3-0 clear.

But the Briton lost focus and loose shots from the baseline allowed her opponent to claw a break back.

Raducanu needed treatment at 3-2 in the first set and was broken again when she returned, with her serve lacking power and potency.

Struggling, she lost five games in a row before snapping the streak with a break, but it was in vain as Kovinic pounced again to take the first set.

The teenager gritted her teeth and played through the pain in the second set and took a 2-0 lead.

She needed more treatment at 3-2 but clung on, using the drop shot and slice to protect the injury as she took the second set.

Both players exchanged breaks in the deciding set before a perfect lob gave Kovinic a second break that proved decisive.