PARIS, France - World No.2 Karolina Pliskova surged up six spots on the WTA Insider Clay Court Power Rankings after winning her biggest clay court title at the Internazionali BNL d'Italia. Reigning Roland Garros champion Simona Halep remains the Queen of Clay, but after another big clay season from No.4 Kiki Bertens, which included her biggest title at the Madrid Open and semifinals in Rome and Stuttgart, the Dutchwoman has closed the points gap on Halep. 

When the 2019 clay season began, Halep had over twice as many points as Bertens on the Clay Court Index, posting a lead of over 2,000 points. As the French Open is set to begin, Bertens has cut that lead to just over 1,100 points. 

The WTA Insider Clay Court Power Index is based on an empirical formula that isolates a player's success rate on clay courts. To measure a player's recent aptitude on the surface, the Insider team applied the following formula, which takes into account a player's results over the last four seasons:

100% of points earned on clay courts in 2019
75% of points earned on clay courts in 2018
50% of points earned on clay courts in 2017
25% of points earned on clay courts in 2016

The resulting sum accounts for a player's "Clay Court Index."

Click here to see where the rankings stood at the start of the clay season. Here's where the Power Rankings stood after Madrid: 

1. Simona Halep: 4,750.50 points (=)
2. Kiki Bertens: 3244.25 points (=)
3. Petra Kvitova: 1,888.00 points (+1)
4. Sloane Stephens: 1809.00 points (+4)
5. Elina Svitolina: 1793.00 points (-2)
6. Jelena Ostapenko: 1651.00 points (=)
7. Garbiñe Muguruza: 1615.75 points (-2)
8. Madison Keys: 1568.25 points (-1)
9. Karolina Pliskova: 1448.75 points (=)
10. Caroline Garcia: 1395.75 (+1)

Recap of 2019's clay court champions so far:

Madrid: Kiki Bertens d. Simona Halep
Rome: Karolina Pliskova d. Johanna Konta
Stuttgart: Petra Kvitova d. Anett Kontaveit
Charleston: Madison Keys d. Caroline Wozniacki
Bogota: Amanda Anisimova d. Astra Sharma
Rabat: Maria Sakkari d. Johanna Konta
Lugano: Polona Hercog d. Iga Swiatek
Istanbul: Petra Martic d. Marketa Vondrousova

With Roland Garros set to begin on Sunday May 26th, here are the Top 20 on the WTA Insider Clay Court Power Rankings as of May 20th:

No.1 Simona Halep (WTA Rank: No.3)
Career Clay Court Win %: 72.5%
2019 Clay Court Record: 7-2 (includes Fed Cup)
Notable recent clay court results: 2019 Madrid Open finalist, 2018 Roland Garros champion, 2018 Rome finalist, 2018 Madrid semifinalist, 2017 Roland Garros finalist, 2017 and 2016 Madrid champion, 2017 Rome finalist, 2016 Roland Garros Round of 16.

No.2 Kiki Bertens (WTA Rank: No.4)
Career Clay Court Win %: 70.5%
2019 Clay Court Record: 12-3
Notable recent clay court results: 2019 Madrid champion, 2019 Rome semifinalist, 2019 Stuttgart semifinalist, 2018 Madrid finalist, 2018 Charleston champion, 2017 Gstaad champion, 2017 and 2016 Nuremberg champion, 2016 Gstaad finalist.

No.3 Karolina Pliskova (WTA Rank: No.2)
Career Clay Court Win %: 59.3%
2019 Clay Court Record: 7-2
Notable recent clay court results: 2019 Rome Champion, 2018 Stuttgart champion, 2018 Madrid semifinalist, 2017 Roland Garros semifinalist, 2017 Rome quarterfinalist.

No.4 Petra Kvitova (WTA Rank: No.6)
Career Clay Court Win %: 67.4%
2019 Clay Court Record: 8-2
Notable recent clay court results: 2019 Stuttgart champion, 2018 Madrid champion, 2018 Prague champion, 2016 Stuttgart semifinalist.

No.5 Sloane Stephens (WTA Rank: No.7)
Career Clay Court Win %: 60.0%
2019 Clay Court Record: 6-3
Notable recent clay court results: 2019 Madrid semifinalist, 2018 Roland Garros finalist, 2016 Charleston Champion.

No.6 Elina Svitolina (WTA Rank: No.9)
Career Clay Court Win %: 63.1%
2019 Clay Court Record: 0-2
Notable recent clay court results: 2018 and 2017 Rome champion, 2017 Roland Garros quarterfinalist, 2017 Istanbul champion, 2016 Roland Garros Round of 16.

No.7 Garbiñe Muguruza (WTA Rank: No.19)
Career Clay Court Win %: 64.1%
2019 Clay Court Record: 2-2
Notable recent clay court results: 2018 Roland Garros semifinalist, 2016 Roland Garros champion, 2017 and 2016 Rome semifinalist, 2017 Roland Garros Round of 16. 

No.8 Jelena Ostapenko (WTA Rank: No.40)
Career Clay Court Win %: 51.1%
2019 Clay Court Record: 3-5
Notable recent clay court results: 2018 Rome quarterfinalist, 2017 Roland Garros champion, 2017 Charleston finalist, 2017 Prague semifinalist.

No.9 Madison Keys (WTA Rank: No.14)
Career Clay Court Win %: 63.6%
2019 Clay Court Record: 6-2
Notable recent clay court results: 2019 Charleston Champion, 2018 Roland Garros semifinalist, 2018 Charleston semifinalist, 2016 Roland Garros Round of 16, 2016 Rome finalist. 

No.10 Caroline Garcia (WTA Rank: No.24)
Career Clay Court Win %: 57.6%
2019 Clay Court Record: 3-4
Notable recent clay court results: 2018 Roland Garros Round of 16, 2018 Rome quarterfinalist, 2018 Madrid semifinalist, 2018 Stuttgart semifinalist, 2017 Roland Garros quarterfinalist, 2016 Strasbourg champion.