Roland Garros 2021 continues to deliver surprise after surprise, especially in the bottom half of the draw, where the lower-ranked players went 4-0 through the Round of 16. Kazakhstan's soft-spoken but big-hitting Elena Rybakina, seeded No.21, tallied the upset of the day, ousting three-time champion Serena Williams 6-3, 7-5.

Match Report: Rybakina stuns Serena to surge into French Open quarterfinals

How did Rybakina, now the highest remaining seed in that half of the draw, pull off the win to make her first Slam quarterfinal in just her third Roland Garros appearance? What does the win mean for the second week of the tournament? And what comes next for Serena? 

WTA Insider breaks down a surprising Sunday in Paris.

Elena Rybakina is appearing in her third Roland Garros main draw and seventh main draw at a Slam.

Photo by WTA/Jimmie48

Elena Rybakina was ready for her moment

It was difficult to predict how the 21-year-old would react playing in her first Slam Round of 16 in her first meeting against, in her own words, the "Legend of the Sport" and 23-time major champion Serena. Yes, Rybakina had not lost a set en route to the fourth round, but she had not faced opposition with anything close to the quality or firepower that Serena could bring. The highest-ranked player Rybakina had faced was No.82 Nao Hibino, whom she beat 6-3, 6-1 in the second round.

In the biggest match of her career, Rybakina handled the moment like a veteran. She prepared by watching extensive video with her analytics-minded coach Stefano Vukov and keyed in on a game-plan to neutralize Serena in the rallies while exploiting her movement.

"We tried to make her play from the backhand side more, just because she has an open stance," Rybakina explained. "With open stance and two hands, it's difficult to move the ball, so I tried to attack this side. Sometimes I was stuck too much to the forehand. That's why I was losing points, because forehand -- it's better not to even play there it's so good."

Getting to Know: Elena Rybakina

Rybakina's tactic worked perfectly, especially on a day when Serena's movement was not at its best. The American was coming in off her best match of the tournament, a straight-sets win over Danielle Collins, but walked out on court with heavy tape around her upper right leg.

"She's powerful, but I was ready," Rybakina said. "Then after few points, I felt it comfortable."

Serena was averaging 25 winners to 26 unforced errors per match in the tournament. Rybakina kept her to 15 winners to 19 unforced errors, with 12 of those errors coming from the backhand. Rybakina also forced 26 errors, 16 from the backhand side. All the while, Rybakina kept her game big and clean. She struck 21 winners to just 13 unforced errors.

Roland Garros doubles partners Elena Rybakina and Anastasia Pavlyuchenkova will play each other for a first Slam semifinal appearance in singles.

Photo by WTA/Jimmie48

There will be a first-time major finalist at Roland Garros

With Serena's exit from the bottom half of the draw, there are just two Top 10 seeds remaining in the draw and they are both in the top half of the draw: last year's champion, No.8 Iga Swiatek, and the woman she beat on Championship Saturday, No.4 Sofia Kenin. It's a notable statistic given a Top 10 seed has won Roland Garros all but four times in the history of the tournament:

1933: Margaret Scriven
2010: Francesca Schiavone
2017: Jelena Ostapenko
2020: Iga Swiatek

With No.33 seed Paula Badosa's win over 2019 finalist and No.20 Marketa Vondrousova and No.31 Anastasia Pavlyuchenkova's win over two-time major champion No.15 Victoria Azarenka, none of the remaining four quarterfinalists in the bottom half of the draw have made a Slam semifinal. In fact, only Pavlyuchenkova has been to the quarterfinal stage at a Slam before. The last time she did it in Paris? In 2011, a decade ago.

Rybakina stops Serena to reach first Grand Slam QF: Roland Garros Highlights

All this is to say, this is an incredible opportunity for the bottom half's final four and an opportunity missed for Serena, who would not have faced a Top 20 player until, at the earliest, the final. 

Serena shifts focus to Wimbledon

After the loss, Serena told reporters she plans to return home to regroup before heading to London, where she will try to win her eighth Wimbledon title and first since 2016. This year sees Wimbledon coming just two weeks after the conclusion of Roland Garros, the first time tours have seen a two-week gap since 2014. 

It's been two years since the last edition of the Championships, when Simona Halep played the match of her life to defeat Serena in the final. Though her clay season may have been disappointing, there are reasons to be positive as she looks to the grass. Her quest for No.24 now moves to a Slam that has seen her walk out to Centre Court on Championship Saturday in each of her past four appearances. 

Grass remains the surface that amplifies Serena's strengths in a way that few others can match. While most players discuss having to adjust and acclimate to the low bounces and unique movement that grass requires, it just seems a natural click for Serena. If clay is the challenge, grass is the comfort. 

"I'm kind of excited to switch surfaces, but historically I have done pretty well on grass," Serena said after the loss. "I have done pretty well on clay, too. Just not this particular season."