To mark the end of an incredible 2018 season, we're counting down the Top 5 WTA tournament matches of the year.

Continuing our countdown is an unpredictable, seesaw battle between two of 2018's highest achievers, where Petra Kvitova garnered a whisker-thin win over World No.1 Caroline Wozniacki in the semifinals of the Qatar Total Open.

Top 5 WTA Matches of 2018:
No.5: Kerber d. Safarova, Sydney

No.4: Bertens d. Halep, Cincinnati
No.3: Danilovic d. Potapova, Moscow International

In February, Caroline Wozniacki came into the 2018 Qatar Total Open on arguably the most celebrated run of form of her career. After capping 2017 by winning the WTA Finals in Singapore for the biggest title of her life to date, the Dane started 2018 by completing her long-running quest for a Grand Slam title, taking the 2018 Australian Open over Simona Halep, and wresting the World No.1 ranking from Halep in the process -- Wozniacki's first stint at the top spot in six years. 

Wozniacki, who held the top seed in Qatar, found herself in the Doha semifinals following a three-set tussle against resurgent Angelique Kerber in the quarterfinals. The Dane had also won her last 12 semifinal matches in a row. Across the net from Wozniacki in the final four, however, was a player who was methodically pulling her way back into the group of elite title contenders, and one who had given Wozniacki fits during their recent history: Petra Kvitova.

At this juncture, Kvitova was less than nine months into her return to activity after suffering severe injuries to her serving hand during a 2016 home invasion. Nevertheless, the determined Czech had already shown that her career would resume its stellar course in 2018. Two weeks before Doha, the former World No.2 claimed the title in St. Petersburg to keep her within striking distance of a return to the Top 20. Kvitova's quarterfinal win in Qatar over Julia Goerges was her 11th victory in a row.

16th-seeded Kvitova had emerged victorious in her last three meetings with Wozniacki, all of which took place on hardcourt, including their first encounter since the Czech's comeback, at Beijing in 2017. But both combatants' recent form set the stage for an unpredictable and tightly contested affair. Wozniacki and Kvitova fulfilled that promise as they battled through a topsy-turvy meeting which was impossible to call until the last point.

Read the match report: Kvitova roars past Wozniacki, gets Muguruza in Doha final

On this occasion, it was Wozniacki who struck first, breaking the Czech twice in the opening set as the top seed's peerless court coverage outdid Kvitova's ferocious forehands. The duo jockeyed back and forth in an intense second set, as Wozniacki was up a break three times and served for the match at 5-4 and 6-5, only to see her delivery broken each time. Kvitova finished off a second-set escape via powerful play in a pivotal tiebreak, capturing the final four points to level the match at one set apiece.

The clash held one more twist, as Kvitova squandered her initial break lead in the deciding set, failing to serve out the match at 5-4. But the Czech had a second chance to serve it out at 6-5, and took the match, 3-6, 7-6(3), 7-5, after a Wozniacki service return flew long on match point following two hours and 40 minutes of grueling play. Kvitova clinched a 12th straight match win -- her first win over a World No.1 of her comeback -- and went on to win the Doha title the next day over Garbiñe Muguruza.

Kvitova propelled her way to the come-from-behind victory by increasing her patience and composure midway through the match, after initially being unnerved by Wozniacki's defensive wizardry. 

“I knew that I need to play aggressive and go for the winners,” the Czech stated during her post-match press conference. “I know that she is catching everything, which she did. And I just probably wasn't as patient with the balls and with all the winners."

“In the second set, when I was still down, I was just trying to calm a little bit and not putting that much pressure on myself and on all the winners, and just try to move her a little bit, but not like crazy," Kvitova explained. "So that's what I tried. I was just counting like point by point and didn't really look to the past or too much forward.”

Kvitova was thrilled that her training since her return prepared her for such a lengthy tilt against the world's best. "[I] just told my coach today that I'm pretty proud of myself, when I was kind of adapting for the outdoor conditions, coming from St. Petersburg and Fed Cup," said Kvitova. "I hoped that all the work which I did in the off-season, hopefully it's just showing up."

"All the fitness which I did, I think [I was] pretty okay today with Caroline," Kvitova added. "I know it wasn't an easy match playing three sets. With Caroline, it's not really pretty easy. So that's where I'm proud of myself."

Wozniacki rued her missed chances in a match decided by extremely narrow margins. “[It’s] definitely disappointing when I had a chance to serve it out twice in that second set,” the Dane said during her post-match presser. “I didn't get many first serves in in the first game, and in the second game she played aggressively and I made a few unforced errors. And I felt that was frustrating because I had my opportunities there.”

"Today I just need to live and learn and try not to make the same mistake when I play her next time, and that's really it," Wozniacki added. "Lots of positives to bring with me." Indeed, after four straight losses, Wozniacki did win their next meeting, a round-robin encounter at the WTA Finals in Singapore in October.

The close encounter was a testament to the top-notch form both Kvitova and Wozniacki demonstrated throughout 2018. Both players continued on from the gripping marathon match to excellent seasons, culminating in berths at this year's BNP Paribas WTA Finals Singapore presented by SC Global for each of them.

For Kvitova, the win was yet another statement that she had cemented her return to top-level tennis. After defeating Muguruza in the Doha final for her second title of the year, she kept on winning, finishing 2018 with five singles titles, more than any other player on the WTA. The two-time Wimbledon champion finished the year ranked No.7, and will try to maintain her Top 10 ranking next year, as well as make a charge towards greater success in the Grand Slam events, where she struggled in 2018.

The remainder of Wozniacki's season, meanwhile, was similar in many respects to Kvitova's, with underwhelming results in the final three Grand Slams, but two additional titles to go alongside her maiden major trophy. The Danish star finished the year at World No.3 for the second straight season, as she prepares for the Australian swing in January as the reigning champion in Melbourne.