After counting down the Top 5 WTA tournament matches of 2018, our year-end review moves to the biggest upsets of the season. In the top spot is Aliaksandra Sasnovich's best win of her breakthrough year - a first-round bombshell at Wimbledon in which the Belarusian stopped title favorite Petra Kvitova at the first hurdle.

Top 5 WTA Upsets of 2018:
No.5: Zhang d. Stephens, Australian Open

No.4: Sabalenka d. Wozniacki, Montréal
No.3: Osaka d. S.Williams, US Open
No.2: Svitolina d. Wozniacki, Singapore

WHAT HAPPENED: The stage was set for one of the most heartwarming narratives in tennis this year to reach its climax at Wimbledon. Two-time winner Petra Kvitova had tentatively returned to the sport just over a year previously from a horrific knife attack sustained in a home invasion during the 2016 off-season; the resultant injuries to her left hand were so severe that there had been fears the much-loved champion would not even be able to hold a racquet again.

Yet Kvitova had defied the odds to not only compete again - but to dominate. Between February and June, the Czech racked up five titles across every surface - St. Petersburg on indoor hard courts, Doha on outdoor hard courts, Prague and Madrid on clay and Birmingham on grass - and compiled a 37-5 win-loss record that included, separately, two of the three longest winning streaks of her career. Coming into her beloved Wimbledon, a tournament where she had been so inspired in the past, Kvitova was about as consensus a WTA Slam title favorite as there has been in recent years.

Read the match report: Sasnovich stuns former champ Kvitova at Wimbledon

The fairytale arc didn't take into account Aliaksandra Sasnovich, though. A less-discussed 2018 narrative was the way in which Belarus's own fairytale run to the Fed Cup final the previous year had springboarded both of its heroines, Sasnovich and Aryna Sabalenka, to new heights this season, with the 24-year-old already notching up a maiden Premier final in Brisbane and breaking the Top 50.

Sasnovich had previously been something of a Grand Slam underachiever - this year's Australian Open marked her first progression beyond the second round of a major - but her flat, powerful groundstrokes, with which she struck 30 winners in this match, had long thrived on fast courts.

Sharper from the outset, Sasnovich would create more chances for herself in the first set, and was rewarded with the crucial break in its penultimate game. But when Kvitova hit back to take the second set by an identical 6-4 score, the Czech seemed to be well on her way to dodging the banana skin - particularly taking into account the formidable three-set record behind her 'P3tra' nickname. But equalizing failed to settle Kvitova's game, with 36 unforced errors counterbalancing 36 winners - and instead it was Sasnovich who peeled away to a stunning bagel set in the decider for a 6-4, 4-6, 6-0 win after two hours and 14 minutes.

WHAT THEY SAID: Early in her career, Kvitova had been renowned for her fearless approach to the big stage, exemplified in her two flawless Wimbledon finals: against Maria Sharapova in 2011 and Eugenie Bouchard in 2014, the weight of the occasion seemed to inspire Kvitova to peak majestically. But despite both the form and the desire she demonstrated elsewhere on Tour in 2018, the former World No.2 ended the season with just a 4-4 record in Slams, having failed even to reach the second week of any.

In a brutally honest press conference, Kvitova admitted that the big stage had become a problem: "When I was kind of younger, I played better on the Grand Slams than the other tournaments," she said. "I think I didn't really care that much before. I do care, unfortunately, now." Consequently, she was unable to play her game: "The nerves were there again," she acknowledged. "I probably didn't really have a clear mind. I [was] kind of thinking little bit too much than I should." 

Nonetheless, having worked so hard to return to the sport, Kvitova was in no mood to catastrophize the loss. "I make a promise that I'm going to be very patient and I'm going to try to break it again for the other side," she vowed.

For Sasnovich's part, the Belarusian was ebullient. "I feel like I can play one more match today!" she declared. "I know that Petra won two times here, so I think it’s a really good experience for me," Sasnovich expanded. "I wasn’t thinking that I would win… I just gave all I could give on the court."

The 24-year-old was also determined to look ahead: "It was a good match, but I think I can play better," she said. "This is just first round. When you come to this tournament, you want to win." 

WHAT IT MEANT: Following her Birmingham title, Kvitova had risen to No.2 in the Porsche Race to Singapore, behind only Roland Garros champion Simona Halep. But even though her five trophies this year would remain a Tour-leading haul for the rest of 2018, the Czech's shock first-round exit put the brakes on her spectacular first-half form: having gone 38-7 prior to Wimbledon, Kvitova's win-loss record afterwards would be a meagre 8-10. And while her season record outside Slams and the WTA Finals would end up at a magnificent 42-10, a winless round robin at the latter meant that it was just 4-7 at the five biggest tournaments on the calendar. Consequently, while Kvitova would regain a Top 4 ranking in October, her year-end ranking would be World No.7 - still a good achievement, but some way off what her first-half results had promised.

Sasnovich, meanwhile, would go on to her maiden appearance in the second week of a major, reaching the fourth round before falling to Jelena Ostapenko. This would be one of the highlights of the Belarusian's long-awaited breakthrough season. Having first broken the Top 100 in 2014, she had spent the next three years floating in and out of it - but in 2018, her upward momentum catapulted her all the way into a year-end placement in the Top 30. Sasnovich, who compiled an overall win-loss record in WTA main draws of 25-20, would also notch up third-round showings at the Australian and US Opens as well as a final in Brisbane, a semifinal at the Moscow River Cup and a quarterfinal at the Kremlin Cup to wrap up her year.