After counting down the Top 5 WTA tournament matches and biggest WTA upsets of 2018, our year-end review moves to the best Grand Slam clashes of the season. Coming in at No.1 is World No.1 Simona Halep's thrilling Australian Open semifinal against 2016 champion Angelique Kerber, battling deep into the final set to emerge victorious, 6-3, 4-6, 9-7, on Rod Laver Arena.

Top 5 Grand Slam Matches of 2018:
No.5: Cibulkova d. Kerber, US Open
No.4: Hsieh d. Halep, Wimbledon
No.3: Serena d. Barty, Roland Garros
No.2: Osaka d. Sabalenka, US Open

WHAT HAPPENED: The stakes couldn't be higher heading into the second semifinal of the 2018 Australian Open. With former World No.1 Caroline Wozniacki awaiting the winner, it came down to top seed Simona Halep and 2016 champion Angelique Kerber, and both had plenty to prove.

Halep finished the 2017 season atop the WTA rankings, and was eager to add a major title to her growing trophy collection after narrow losses at Roland Garros to Maria Sharapova and Jelena Ostapenko. She arrived to Melbourne without a clothing sponsor and found herself down three match points to Lauren Davis before pulling out a 15-13 final set win just to make the second week.

Read the match report: Halep saves match points, ousts Kerber in Aussie epic

Kerber was even more of an underdog after plummeting from the No.1 ranking in 2017, ending a rough season outside the Top 20 for the first time since her initial career ascent six years ago. Over the off-season, the German hired famed coach Wim Fissette (formerly with Halep, Johanna Konta, and Victoria Azarenka, among others), a move that immediately paid dividends as Kerber captured the Apia International Sydney ahead of the Australian Open.

The pair played five times in 2016, with Kerber winning four of those encounters, making Halep's fast start all the more surprising on Rod Laver Arena. From a quick 0-5 deficit, the German was very much in the match from there, rallying from a set and break down to level the match at a set apiece.

Playing her first Australian Open semifinal, Halep relied on her stellar footwook to edge ahead in the decider, serving for the match at 5-3 and holding two match points on Kerber's serve in the following game.

The former No.1 saved both and quickly turned the tables on Halep two games later with match points on her own serve. Navigating through longer and longer rallies, the Romanian remained calm - her biggest improvement under coach Darren Cahill - and kept fighting to become the first from her country to reach the final in Melbourne after two hours and 20 minutes.

WHAT THEY SAID: For Halep, it was a major mental victory after the disappointment of last year's loss to Ostapenko in Paris.

"I just had confidence in myself. I told myself to fight for every point and then rest afterwards. I tried to stay calm but today I was like a roller coaster. I didn't give up though and, if you don't give up, you can win matches. I am proud of myself."

"It's not easy, because I was a little bit too negative before, so I'm trying to change that," she continued in her post-match press conference. "I changed already, but I need to work on it more. I want to improve more, and for sure, if I will be focused on this thing, I will be much better in the future."

As for Kerber, the loss was tempered by the trends, and it was clear from her Australian summer that she was trending up towards her best tennis in 2018.

"I gave everything," she said after the match. "This is what I will tell myself in the next few days. Looking back on what I achieved in the last three weeks it was not so bad. I mean, when I look back, like, four, five weeks ago, and had somebody told me that I would win so many matches in a row, winning a title, being in the semis here and still having the opportunity to win this match, as well.

"I think I will just take the positive things from the last three, four weeks and I'm looking forward."

WHAT IT MEANT: The match between Halep and Kerber ultimately foreshadowed much for the next few major tournaments, though neither would lift the Daphne Akhurst Trophy. Halep took a tough loss to Wozniacki in the championship match, only to finally make good on her Grand Slam potential at Roland Garros, where it all began for the Romanian.

Down a set and a break to Sloane Stephens, Halep roared back to finally hold the Coupe Suzanne Lenglen and receieve a hero's welcome at the Bucharest National Stadium. 

"The fact that I could be No.1 in the world last year gave me confidence and gave me a little bit of relief," Halep explained, "because I touched something, something big, something huge, and I just had in my mind to win a Grand Slam after that. So the ranking didn't matter anymore.

"The fact that I'm No.1 now and winning a Grand Slam makes me very, very happy and makes me thankful for everything that I have done, everything that I have received from the people, all the love, all the support."

Kerber's time came three weeks later at Wimbledon, where she avenged a 2016 defeat to Serena Williams to win her third major title and first at the All England Club. With Australian Open and US Open titles already in the books, Roland Garros is all that remains for her to capture the Career Grand Slam - not that the notoriously clay-allergic Kerber is thinking much about it.

"I think we have to see in the future. I think that's a longer way to go for it," she joked after the match.