After counting down the Top 5 WTA matches and Top 5 Grand Slam matches of 2017, our year-end review moves to the biggest upsets of the season.

No.2 on the countdown comes from the magical run of Mirjana Lucic-Baroni in Melbourne, as the Croat defeated Karolina Pliskova to reach her first Grand Slam semifinal in nearly 20 years.

WHAT HAPPENED: When Mirjana Lucic-Baroni took the court against No.5 seed Karolina Pliskova in the quarterfinals of the Australian Open, the Croat was already turning back the clock.

Ranked World No.79, Lucic-Baroni put together a magical run in Melbourne, defeating Wang Qiang, Agnieszka Radwanska, Maria Sakkari and Jennifer Brady to reach the second Grand Slam quarterfinal -- 18 years after her first.

Both wiser, and a survivor, this time around, the 34-year-old Cinderella was set to take on Pliskova, dubbed one of the conteders for the women's trophy after a breakout run to the final of the 2016 US Open and a lead-up title at the Brisbane International.

Lucic-Baroni came from a set down in two of her first four matches, against Wang and Sakkari, but the veteran hardly faced adversity in the early stages of the match.

The unseeded Lucic-Baroni routinely came out on top of heavy-hitting baseline exchanges against the Czech No.1, building a one-set advantage in the last eight matchup.

Nonetheless, Pliskova - who was looking to build on both a career-best Australian Open and success at Grand Slam level - hit back to level the match at one set apiece taking advantage as Lucic-Baroni's level dipped, and the Croat began to struggle with a leg injury.

Facing a 4-3 deficit, Lucic-Baroni took a medical timeout late in the third set, and dug deep to win the final three games, securing a stunning 6-4, 3-6, 6-4 victory to secure her place in the last four.

Almost as stunning as the victory for the World No.79 was the location in which she pulled it off: rather than at Wimbledon, where she made her last semifinal as a 17-year-old in 1999, or at the US Open, where she reached the fourth round in 2014 to begin her career revival, this was Melbourne.

The Croat had lost eight of nine matches in previous trips to the Australian Open, but Lucic-Baroni won five matches at the tournament to reach the final four.

Read more: Top 5 Upsets of 2017
No.5: Osaka vs. Kerber, US Open
No.4: Bellis vs. Radwanska, Dubai Duty Free Championships

No.3: Krunic vs. Konta, US Open

WHAT THEY SAID: Filled with perspective on her long road back to the spotlight, an emotional Lucic-Baroni reflected on where she'd been -- and how far she'd come -- over the past two decades. 

Read more: Lucic-Baroni blasts past adversity for full circle moment in Melbourne

"This time, it's incredibly special, especially since it's been so long since the last time I've been in semifinals. 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," she said.

"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."

That fresh perspective not only helped the former wunderkind thrive in her new life, but also held her in good stead when she wanted to return to the court -- believing she had more to give.

"When I was younger, I just believed because I won a lot and it was that confidence you simply have because you're winning all the time," she said. "When you stop winning as much and you don't play for a long time, you definitely lose it a little bit. Not even lose it, you forget it. You forget deep down kind of who you are on the court.

"That happened to me a little bit, where I struggled for a few years, and I'm really glad that I remembered. At 34 years old, like I said before, I have a wonderful home. I'm happily married. I would be perfectly okay being at home enjoying my family.

"I really knew deep down in my soul that I have these results in me. To now be here and actually live these moments, it's incredible."

WHAT IT MEANS: After victories by both Venus and Serena Williams -- who would eventually meet in the final -- Lucic-Baroni was one of three 30-somethings in Melbourne's final four.

Though she'd lose to Serena in straight sets in the semifinals, Lucic-Baroni's magical Melbourne fortnight helped her set new milestones as a WTA veteran.

She eclipsed her previous career-best ranking after the fortnight, rising to No.29 on Jan. 30: past her previous best of No.32 -set in May of 1998.

She later reached a high of World No.20 in May, and though she struggled with injuries for much of the rest of the season, her other highlights included a quarterfinal in Miami, a semifinal in Charleston at the Volvo Car Open, and a third round result at the Internazionali BNL d'Italia in Rome.

Pliskova proved unfazed by the opportunity that passed her by in Melbourne, as she went on to reach her first Grand Slam semifinal in Paris at Roland Garros. She also won two more titles in the 2017 season, en route to becoming one of five women to hold the World No.1 ranking.