SAP Inside the Numbers is an ongoing series which looks to preview and reflect on the tour's major swings throughout the season. With the clay season in the books, SAP and WTA Insider dig deeper into the numbers to recap a hotly contested clay-court swing, which saw World No.1 Simona Halep cement her status at the top of the game. 

Simona Halep became the first woman to win her maiden major as a reigning No.1. (Getty Images)

2018 Clay Court Champions

French Open: Simona Halep d. Sloane Stephens, 3-6, 6-4, 6-1.

Petra Kvitova became the 1st woman to win the Mutua Madrid Open three times. (Getty Images)

Madrid: Petra Kvitova d. Kiki Bertens, 7-6(6), 4-6, 6-3
Rome: Elina Svitolina d. Simona Halep, 6-0, 6-4
Stuttgart: Karolina Pliskova d. CoCo Vandeweghe, 7-6(2), 6-4
Charleston: Kiki Bertens d. Julia Goerges, 6-2, 6-1

World No.15 Elise Mertens ran a 14-match win-streak during the clay season.

Prague Open: Petra Kvitova d. Mihaela Buzarnescu, 4-6, 6-2, 6-3
Strasbourg: Anastasia Pavlyuchenkova d. Dominika Cibulkova, 6-7(5), 7-6(3), 7-6(6)
Rabat: Elise Mertens d. Ajla Tomljanovic, 6-2, 7-6(4)
Lugano: Elise Mertens d. Aryna Sabalenka, 6-1, 6-3
Nuremburg: Johanna Larsson d. Alison Riske, 7-6(4), 6-4
Bogota: Anna Karolina Schmiedlova d. Lara Arruabarrena, 6-2, 6-4
Istanbul: Pauline Parmentier d. Polona Hercog, 6-4, 3-6, 6-3

Simona Halep and Elise Mertens Tally Most Clay Court Wins in 2018

Roland Garros champion Simona Halep and Belgium's Elise Mertens, who won two clay titles over the spring, topped the leaderboard for clay-court wins with 16 apiece. Halep, who was also a finalist in Rome, finished with a 16-3 record, while Mertens finished with just two losses on the dirt. 

The difference between the two win-leaders came in the strength of competition. Halep played four clay-court events, all Premier-level or higher, with an average rank of opponent of 43.26. Mertens also played four clay events, two of which were International level tournaments, which she won. She posted an average rank of opponent of 102.56.

Simona Halep, Sloane Stephens, and Petra Kvitova Make Points Gains 

Twelve months ago, Sloane Stephens was in the 10th month of her injury layoff, having been sidelined due to foot surgery. Roland Garros had always been Stephens' most consistent major, after making the Round of 16 in four straight appearances from 2012 to 2015. Fit and firing again, the reigning US Open champion found her clay legs quickly in Paris and her standout run to her 2nd major final in the last 3 Slam gives her a large point cushion as she prepares to defend a large chunk of points over the summer.

Impressively, Petra Kvitova, Madison Keys, and Karolina Pliskova cleaned up on clay, a surface each will fully attest is not their best. Kvitova won 13 consecutive matches on clay en route to titles in Prague and her record-breaking 3rd title in Madrid. Pliskova won her 1st Premier title on clay by winning Stuttgart, while Keys' strong run to her 2nd Slam semifinal of the last three majors was a welcome surprise. 

Looking at Halep's comparative numbers on clay between her strong 2017 season - which saw her go 18-3 but fall short in the Roland Garros final to Jelena Ostapenko - and her Slam-winning 2018 season, the Romanian's incremental gains on both serve and return are notable. Already the overall tour-leader in Return Points Won (50.4%) and Return Games Won (50.2%) this season, Halep was also far more clutch in 2018, posting better break point and three-set numbers.

The World No.1 came into the clay season with a 7-2 record in three-set matches in 2018. She comes out of the clay season with a share of the tour-lead in three-set match wins, posting a sparkling 13-2 record (tied with Kvitova) after going 6-0 on clay. Three of those wins came in Paris, where Halep rallied from a set down to defeat Alison Riske in the first round, Angelique Kerber in the quarterfinals, and Stephens in the final. 

Julia Goerges and Karolina Pliskova leave the clay season a No.1 and No.2 on the ace leaderboard. (Jimmie48/WTA)

More Clay Season Notes:

- Ace Queens: Julia Goerges and Maria Sharapova tied for the most aces hit in a single match on clay. Goerges struck 17 against Dominika Cibulkova in her 6-4, 5-7, 6-0 win in the first round of Roland Garros. Sharapova fired 17 in her 3-6, 7-6(6), 6-4 loss to Caroline Garcia in the first round of Stuttgart.  

Kristyna Pliskova hit the most aces during the clay season and added one more statistical notch to her belt: Pliskova fired 15 aces against Serena Williams in the first round of the French Open, the most aces hit against Serena since match stats have been recorded in 2008.

2018 Clay Season Ace Leaders: 

108: Kristyna Pliskova (15 matches)
100: Julia Goerges (13 matches)
94: Karolina Pliskova (14 matches)
77: Maria Sharapova (14 matches)

Goerges leaves Paris atop the 2018 Ace Leaderboard, hitting 225 aces in 31 matches so far. 

- Fewest games lost en route to a title: Elise Mertens. The Belgian lost just 21 games over five matches to win the title in Rabat. That is the fewest games lost on any surface en route to a title so far in 2018.

- The Dominants: Of the 12 titles on the line during the clay season, 7 were won by a Top 5 seed.

After winning her first title in 10 years, Pauline Parmentier progressed to the third round of the French Open. (Getty Images)

- Always full of surprises: The 2018 clay season featured three surprise title winners who also became the three lowest-ranked players to hoist trophies so far this season:

No.132 Anna Karolina Schmiedlova, Bogota
No.122 Pauline Parmentier, Istanbul
No.97 Johanna Larsson, Nuremberg

At 32 years old, 2 months, and 28 days, Parmentier is also the oldest champion of the season so far. 

- Rise and Grind: 6 of the 8 longest matches of the season so far came on the clay. Top prize goes to Anastasia Pavlyuchenkova and Dominika Cibulkova, who played the longest non-Slam match of the season in the final of Strasbourg. The Russian prevailed 6-7(5), 7-6(3), 7-6(6) to win her 1st title of the season. 

The match also set the mark for the most games played in a non-Slam match this year: 39.