To mark the end of a record-setting 2019 season, wtatennis.com 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.2 is 15-year-old Coco Gauff's Grand Slam debut - a 6-4, 6-4 defeat of Venus Williams in the first round of Wimbledon.

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: The first-round clash between the oldest and youngest players in the Wimbledon draw was one that most observers had highlighted - but more out of curiosity than expectation of a surprise. Sure, 15-year-old Coco Gauff had made waves the previous week, becoming the youngest player to come through Wimbledon qualifying in the Open Era. And sure, 39-year-old Venus Williams was now unseeded, having fallen to World No.44 and not having made a semifinal in 15 months. But this was still a mismatch on paper: a five-time Wimbledon champion back on the lawns where she has come alive so often in the past, against the World No.313 who was not yet a year out of her junior career. There was an easy narrative around the match - Gauff had declared after winning her final qualifying match that she would most love to play either Serena or Venus Williams, whom she had grown up idolizing, in the main draw. The actual result, though, was a foregone conclusion to most beforehand.

Initially, it was impressive enough to see that Gauff, far from being overwhelmed in her first match on such a big court, in such a big tournament and against such an illustrious opponent, was actually staying with Williams. And then in the fifth game matters began to take a turn for the unexpected: conjuring up a brilliant lob en route, the teenager seized the first break. Gauff's defence, the cornerstone of her game, was a marvel: she was able to track down almost everything Williams could power at her, and showed remarkable hand skills to control the ball on the run. When she got a chance to bury the ball, Gauff didn't shy away, either, with her smooth backhand repeatedly nailing shots that left Williams flailing.

But it was also the 2018 Roland Garros junior champion's self-belief that was extraordinary. She had told reporters as she made her way through qualifying that she feared no opponent, and she demonstrated just that as, pumping her fist and letting out a determined "Come on!", she strode to her chair after wrapping up the first set.

That quality would be even more necessary in the second set. Once again, Gauff grabbed the first break against Williams, who was unable to stem her flow of errors. But the former World No.1 hit back this time, summoning all of her notorious fighting qualities to level the score at 4-4. This was the point at which so many inexperienced players, faced with a legendary name on the other side of the net, have felt their self-belief falter. Not Gauff - who survived a riveting dénouement the hard way. Williams had two points to hold for 5-4 - but Gauff would come through a two-deuce tussle to regain her lead. Serving for the match, the youngster would let three match points slip before Williams held another break-back point - but again, it was the rookie who kept a cool head. A final Williams forehand found the net on Gauff's fourth match point - and a contest that should have been a curio was instead a seismic upset that was emblazoned across front pages worldwide the following day.

Read the match report: ‘My dream was to win. That's what happened’: 15-year-old Cori Gauff stuns Venus Williams in Wimbledon debut

WHAT THEY SAID: Williams was as complimentary of her young opponent as she was dissatisfied with her own performance. "She did everything well today," said the former champion. "She put the ball in the court, which was much better than I did. She served well, moved well. It was a great match for her... She played so well. Even all the shank balls went in. I actually didn't play well. It was a contrast of both sides."

Gauff, however, was over the moon - and her excitement was contagious in a press conference that also ranged from rapper Miss Mulatto, the teenager's walk-on music, to her favorite "And I oop!..." meme. "Obviously I'm super shocked," Gauff gushed. "I literally got my dream draw, so I'm just super happy I was able to pull it out today."

When it came to talking tennis, though, Gauff was all business, displaying once again the prodigious self-assurance she had already shown off in qualifying. "If I went into this match saying, Let's see how many games I can get against her, then I most definitely would not have won," she pointed out, reiterating that her long-term ambition is to be "the greatest". Continuing, Gauff summed up her approach concisely, making it seem simple: "My goal was to play my best. My dream was to win. That's what happened."

Read more: 'A roller coaster that didn't come down' - Gauff reflects on Tour debut and improvements for 2020

The key was more mental than strategic for the youngster. "I didn't really have a strategy on how to play her," Gauff revealed. "My goal was to stay calm and composed. I really believe when I do that, I can do anything. I like to figure things out on the court. My parents just always tell me, If you play your game, you can beat anyone."

For Gauff, self-confidence is not just a tennis philosophy but a life one. "I think people just limit themselves too much," she said. "Once you actually get your goal, then it's like, What do you do now? I like to shoot really high. So that way I always have many goals along the road, but that way you have the ultimate goal."
And the prodigy's ultimate goal for her Wimbledon debut? "To win it," naturally.

Coco Gauff - Wimbledon 2019 - Getty

Getty

WHAT IT MEANT: Prior to this match, the name Coco Gauff had been bandied around by tennis insiders for a few years. But overnight, her fame exploded: her youth, the primetime stage and the passing-of-the-baton narrative combined to spark Gauffmania, a tidal wave of attention that went from zero to 100 overnight.

The subject of the frenzy was able to back it up, though. Gauff would go on to reach the fourth round of Wimbledon, with two further contrasting wins demonstrating her versatility and mentality: in the second round, the qualifier survived the grass-court nous of 2017 semifinalist Magdalena Rybarikova, who had upset Aryna Sabalenka in the first round, and in the third round she came from a set down and saved two match points in a riveting encounter with Polona Hercog. It took eventual champion Simona Halep to ultimately stop Gauff.

The Gauff train didn't stop on her return home to the USA, either, as the game's newest star put together another pair of dramatic showcourt comebacks to reach the third round of the US Open. And then, perhaps even more impressively, she proved she could excel out of the Grand Slam spotlight as well. In Linz, as a lucky loser in the main draw, Gauff ploughed through a field that included her maiden Top 10 victory over Kiki Bertens to lift her first ever trophy. Having ended 2018 at World No.875, this run would rocket Gauff into the Top 100 to finish her breakthrough season at World No.68.