Elina Svitolina (UKR #20) vs. [11] Petra Kvitova (CZE #14)
Head-to-head: Kvitova leads, 2-1
Key Stat: There has only been one unseeded medalist in women’s singles since tennis returned to the Olympics in 1988 (Alicia Molik, Bronze, 2004).

Chaos reigned supreme at the top of the draw on Tuesday in Rio, as Elina Svitolina completed the upset to end all upsets by knocking off four-time Olympic gold medalist Serena Williams in straight sets. It was a monumental victory for Svitolina, who admitted afterwards that she dared not dream of defeating Williams. “It’s one of my dreams to play against her, and to beat her – I don’t think I was even dreaming about that,” the elated 21-year-old said after the match. Now, for the challenge of recalibrating emotionally to face a menacing Petra Kvitova for a spot in the semifinals. Kvitova showed true Olympic spirit in gutting out a see-saw three-setter with Ekaterina Makarova on Tuesday, and the Fed Cup legend has always taken her game to another level when representing her country in the past. Will she continue to elevate her tennis and engineer a season-changing run to the medal round, or will the 21-year-old Ukrainian continue to prove to be a player of destiny this week in Rio?

Pick: Kvitova in three

[2] Angelique Kerber (GER #2) vs. [10] Johanna Konta (GBR #13)
Head-to-head: Kerber Leads, 1-0
Key Stat: Kerber and Laura Siegemund are bidding to become the first German women to medal at the Olympics since Steffi Graf in 1992.

Two of tennis’ most in-form and mentally tough players will square off in a high-stakes quarterfinal that marks their second meeting of 2016. Angelique Kerber eased past Johanna Konta in this year’s Australian Open semifinals, and that victory proved not only to be a springboard to a first major title, it also has provided a layer of belief that has further solidified Kerber’s presence at the top of the game. On Tuesday Kerber worked her way past Samantha Stosur in straight sets while Konta had to scratch and claw to end Svetlana Kuznetsova’s Olympics in a three-hour and seven minute battle. Konta is just two weeks removed from her first career title at Stanford and she’ll no doubt be eager to prove that she has the ability to match wits and strokes with a player of Kerber’s caliber. She wasn’t up to the task against the German in January – will she find a way past her on Wednesday?

Pick: Kerber in three

Monica Puig (PUR #34) vs. Laura Siegemund (GER #32)
Head-to-head: First Meeting
Key Stat: Puig and Siegemund were ranked 90 and 92 respectively at the start of the season.

My, how fortunes can change over the course of a season. Monica Puig and Laura Siegemund, two players who began the season barely inside the Top 100, will play for a spot in the medal round on Wednesday in Rio. As unlikely as it sounds, when one considers the amount of progress that Siegemund and Puig have made over the course of the last seven months, this quarterfinal is not all that improbable. The pair own a combined 9-9 record vs. the Top 20 this season, and both have gone deep into draws more consistently than ever. Puig notched the second biggest shock of Day 4 when she shellacked Spain’s Garbiñe Muguruza, 6-1, 6-1. Puig matched Muguruza’s winner count and committed half the errors in a tidy performance. “I consider it the biggest win of my career because it’s at the Olympics,” she said after the match. “Right now, I’m in the clouds. I can’t even believe it because truly it was incredible.” Will Puig be able to recover mentally to take on the feisty Siegemund with so much at stake? Or is it the 28-year-old German who will seize the day and a surprise trip to the medal round?

Pick: Siegemund in three

[7] Madison Keys (USA #9) vs. Daria Kasatkina (RUS #27)
Head-to-head: First Meeting
Key Stat: Keys has won back-to-back three setters in her last four events.

The two youngest players remaining in the draw will square off in a matchup that tennis fans will likely see—and enjoy—quite a bit over the next ten years. No. 7 seed Madison Keys has had her mettle tested early and often here in Rio, but each time she has been pushed, the 21-year-old power broker has pushed back, gutting out back-to-back three setters in her last two matches and showing poise and patience to go with her world-class attack. Speaking of poise, 19-year-old Daria Kasatkina has proven to be a quick study on the Olympic stage. The Russian methodically eased past Italy’s Sara Errani to reach the quarterfinals on Tuesday, proving once again that she’s every bit as good as her ranking, and perhaps even better. But how will Kasatkina handle the grooved ground game of Keys? Will she be able to keep the hard-hitting American off balance, or will she find herself in over her head against a blossoming American who is willing to lay everything on the line in the quest for an Olympic medal?

Pick: Keys in three

Around the Grounds:

The women’s doubles quarterfinals will also be held on Wednesday. Russia’s Daria Kasatkina will perform double duty alongside Svetlana Kuznetsova in a battle against No. 6 seeds Lucie Hradecka and Andrea Hlavackova of the Czech Republic. Switzerland’s Martina Hingis and Timea Bacsinszky will look to upend the Chan sisters of Chinese Tapei in a battle of Top 5 seeds. See the complete doubles draw for matchup information here.

By the Numbers:

19 – The age of Russia’s Daria Kasatkina, who is the youngest player left in the draw.

34 – Ranking of Monica Puig, who is the lowest-ranked participant in the women’s singles quarterfinals.

2 – Germany is the only country to boast two women’s singles quarterfinalists.