To mark the end of a record-setting 2019 season, is counting down our picks for the best WTA Upsets of the Year. Check out our Top 5 Grand Slam Matches and our Top 5 WTA Matches here.

Coming in at No.1 is Taylor Townsend's unlikely upset over reigning Wimbledon winner Simona Halep, saving a match point to thrill the Arthur Ashe Stadium crowd, 2-6, 6-3, 7-6(4).

Top 5 WTA Upsets of 2019:
No.5: Kenin d. Barty, Toronto
No.4: Azarenka d. Svitolina, Rome
No.3: Andreescu d. Kerber, Indian Wells
No.2: Gauff d. V.Williams, Wimbledon

WHAT HAPPENED: Long before Coco Gauff served notice as a talented teen, Taylor Townsend was the young American on the rise, becoming one to watch at the start of the decade when she pushed Laura Robson to three sets at the 2011 US Open qualifying tournament. A few months later, she became the first American since Lindsay Davenport to win the singles and doubles titles of a junior Grand Slam tournament at the Australian Open. Townsend turned heads as much for the way she won as the victories themselves, employing a once ubiquitous - now borderline arcane - style of serve-and-volley tennis replete with a variety of slices and spins.

Competing with the power game that has taken over the WTA tour, Townsend struggled for consistency as she transitioned from the junior rankings, making just one Grand Slam third round appearance at the 2014 French Open. Strong results on the ITF Pro Circuit helped her become a fixture of the Top 100, but the American was lacking a signature result, a statement victory that could reassert her style - last seen by the the likes of Martina Navratilova - towards the top of women's tennis.

Townsend got her chance playing former World No.1 Simona Halep in the second round of this year's US Open. She was two points from defeat in her final round qualifying match against Nina Stojanovic, and rallied from another set down against Kateryna Kozlova to play Halep, against whom she had never won more than three games in any of their previous six sets.

Halep was on a roll at major tournaments, shocking 23-time Grand Slam champion Serena Williams to win Wimbledon, and outbattled Townsend's countrywoman Nicole Gibbs in her first round match.

Read the match report: 'It's been a really long journey' - Qualifier Townsend stuns Wimbledon champ Halep at US Open

Townsend rushed past all the signs pointing towards a quick defeat, and headed straight for the net. The 23-year-old turned her game up to its highest power, approaching the net an absurd 106 times (winning 64 of those points) in what would become a three-set tussle. Even knowing the result, the strategy sounds reckless against a dynamic counterpuncher capable of absorbing the American's pace and redirecting into the open court.

Such skepticism underplays the importance of the stage; where Townsend was playing with the home crowd at her back, Halep was at the epicenter of her least successful Slam. Despite her hardcourt prowess, the two-time major champion has been open about her battle to find peace in the city that never sleeps. Where Townsend was on fire, Halep was uninspired, helping the hometown favorite to slowly turn the tables on the Romanian, emerging from an exchange of breaks in the second set to level the match.

Townsend broke again in the third and held two match points on her hitherto indomitable serve before Halep reversed the deficit to find herself a point from victory. Undaunted by the occasion, Townsend saved the match point and forced a tie-break; from 3-3 in the Sudden Death, she was all but unstoppable to secure two hour and four minute victory.

WHAT THEY SAID: For many, it was a full circle victory. While Townsend validated that premise, she also felt it was a testament to a quick improvement from Wimbledon, where she narrowly lost to another Top 10 player in Kiki Bertens - having held a match point.

"I think for so long that's been my whole thing, just continue to press forward and just realize that I belong on this level," she said after the match. "You know what I mean? I've had a lot of people doubting me being able to 'break through,' quote unquote.

"It's just confirmation more for myself that I'm on the right path, doing the right things. You keep your head down and keep working and you see what happens."

Her audacious style, she explained, was Townsend at her most natural.

"I was always doing weird stuff, chipping middle shots on the forehand side. I was doing crazy stuff. It was what I enjoyed doing. I always enjoyed coming to the net. It's always a fine line, especially as you move up and through the levels, that you have to kind of hone in and have things that you do well. You have strengths, but you have to be solid from a certain point because these players are just too good. The level only gets higher."

She also recalled a conversation with Halep from just a few months earlier, shortly after the pair played a more perfunctory match at the Miami Open.

"Something inside of me was nudging me to, like, ask her. I was, like, 'Screw it, let's see what she felt on the other side of the net.' I know what I felt, but I was curious to see what she felt.

"Honestly, she didn't really tell me anything I didn't know, but it was good to hear it from another player, someone I just played, played a couple of times, and especially someone who is at such a high level, has accomplished so much.

"I'm not saying that everything she said I implemented into my training, but it was definitely in the back of my head to remember what she said and also remember why I asked, what drove me to ask that question, kind of that hunger and desire to get better.

"I think I kind of turned that into more of a positive to say, Hey, you can continue to learn and grow."

Halep also remembered the chat, joking, "Next time I will not say anything," in her post-match press conference.

"I had expectations from myself that I'm confident and I feel the game. But today was different. I was very close. I had match ball. But, you know, sometimes it happens. I have just to look forwards. I'm Wimbledon champion, so I will not ruin that."

WHAT IT MEANT: It would have been easy to expect a letdown from Townsend, especially as she next faced another solid baseliner in Sorana Cirstea, who would surely anticipate the qualifier's net-rushing approach. Instead, Townsend put on a mature display to knock out Halep's compatriot in straight sets and reach her Grand Slam fourth round

"That Taylor is in the garbage," she said of her old self. "The hair, all of it. Gotta go.

"You never know when things are going to happen. You continue to work and you continue to kind of pluck away. And some people's paths and some people's, ultimately their journey, everyone's journey is different. Some people's happens quicker than others. Mine took, what? Six, seven years? I feel better than ever before. I'm just thankful for where I am now and kind of the things I had to go through in order to be here and appreciate where I am."

Townsend treated the American crowd to one last Arthur Ashe thriller, forcing eventual champion Bianca Andreescu to three sets under the lights

While Halep shook off the shock ahead of the Asian Swing, an acute injury at the Dongfeng Motor Wuhan Open stunted her fall schedule, though she ultimately recovered to play one of the best matches of the season at the Shieseido WTA Finals Shenzhen. With just one run to the semifinals back in 2015, the US Open is the lone major tournament where Halep is yet to make the final; whether she can break new ground in the Big Apple will have to wait another year.