She is the Cinderella story of the Australian Open but Mirjana Lucic-Baroni doubted whether she could finish her quarter-final against Karolina Pliskova as pain set in.

Comeback queen Lucic-Baroni advanced to her first grand slam semi-final in 18 years after upstaging fifth seed Pliskova 6-4, 3-6, 6-4 on Wednesday.

Bruised and battered, unheralded Lucic-Baroni defied the odds in her first quarter-final appearance since 1999 as she set-up a showdown with Serena Williams.

In a topsy-turvy match, the 34-year-old required a medical timeout in the final set but returned to win the final three games with only one point dropped to end any doubts.

"I was just really thankful, really thankful to God that I was able to do this, that I was able to finish my match," Lucic-Baroni told reporters. "I was really worried. I was concerned. I didn't know if I had it in me to finish it.

"I started hurting pretty bad mid-match, especially towards the end. The fact that I was able to do it and so well at the end, I was really grateful."

She continued: "I was really concerned with my physical wellbeing at that point. And I just said to myself, I said, they're either going to wheel you out. I mean, I'm not going to give up, just keep fighting. And that was it.

"I just kept encouraging myself to keep going, to stay strong."

Despite publicly voicing her concerns, the Croatian has no problem about backing up against the 22-time grand-slam champion on Thursday.

"Every day I've played. I haven't had a day off in weeks. I don't know the last time I had a day off. I played every day singles and doubles," she added.

"I'm going to be just fine. I'm going to recover, do some therapy, and I'll be fine. I'll just put some extra tapes on and hopefully it will hold me together. I'll fight hard. I'll be okay."

After well-documented personal and financial problems, Lucic-Baroni is now flying high amid her fairytale run.

A junior grand-slam winner at the US Open (1996) and Australian Open (1997), Lucic-Baroni is now one win away from a remarkable maiden major final following her semi-final appearance at Wimbledon in 1999 and she is savouring every moment.

"It's incredibly special, especially since it's been so long since the last time I've been in semi-finals," Lucic-Baroni said. "And the struggle has been so much bigger, and nobody in this world thought I could ever be here again, beside my closest family, my coach, and my brothers, my sisters, my husband, my mom. Beside my little circle, I don't think anybody believed that I could do it. And it's really fun.

"It's fun to prove everybody wrong, and it's fun to enjoy this for myself and live these incredible moments. It's more special this time, for sure."