Major Threat: Simona Halep, Serena Williams lead 10 best performers at recent Slams

Not all tournaments are created equal. It's no surprise that the marquee names in the sport all possess the uncanny ability to bring their best on the biggest stage at the sport's four major tournaments. 

With the 2019 US Open around the corner, who are the most reliable players over recent years at the majors? 

To evaluate a player's strike rate at the Slams, the WTA Insider Team applied the same empirical formula used to determine the surface-specific WTA Insider Power Rankings. To measure a player's recent aptitude at the majors, the Insider team applied the following formula, which takes into account a player's results over the last four seasons:

100% of points earned at Slams in 2019
75% of points earned at Slams in 2018
50% of points earned at Slams in 2017
25% of points earned at Slams in 2016

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

Simona Halep and Serena Williams top the list at No.1 and No.2, with each beating out the rest of the field in the number of quarterfinals made over the four year span (Halep: 8, Serena 9). The pair have faced off twice this year, both at the Slams, and split results. Serena got the better of Simona in the Australian Open Round of 16, and Halep earned her revenge last month in the Wimbledon final. Three-time major champion Angelique Kerber also features high on the list. In fact, only Serena (12,080 points) has earned more overall points at the Slams over the last four years than Kerber (8,970 points). 

Also featuring on the Top 10 list are the two youngest additions to the Club of Champions. Twelve months ago, neither Naomi Osaka or Ashleigh Barty had made it past the Round of 16 at a major. Osaka is now a two-time major champion, while Barty followed up her major breakthrough after making the Australian Open quarterfinals this year, by winning Roland Garros. 

The list includes two women who are still chasing their first major titles, but whose Slam bona fides are well-established. Sitting at No.5, Karolina Pliskova has made 7 major quarterfinals over the four-year span, third only to Halep and Williams. At No.6 is Madison Keys, who has made 5 major quarterfinals in her last 8 Slam appearances, the best rate of any player over that stretch.

Here's the full Top 10 list: 

1. Simona Halep
Slam Index: 6,402.5
Slam Quarterfinals made over span: 8
Best Slam results over span: 2019 Wimbledon Champion, 2018 Roland Garros Champion, 2017 Roland Garros finalist, 2018 Australian Open finalist.

2. Serena Williams
Slam Index: 6,3445.0
Slam Quarterfinals made over span: 9
Best Slam results over span: 2017 Australian Open Champion, 2016 Wimbledon Champion, 2019 Wimbledon finalist, 2018 US Open finalist, 
2018 Wimbledon finalist, 2016 Roland Garros finalist, 2016 Australian Open finalist, 2016 US Open semifinalist.

3. Angelique Kerber
Slam Index: 4,402.5
Slam Quarterfinals made over span: 6
Best Slam results over span: 2018 Wimbledon Champion, 2016 US Open Champion, 2016 Australian Open Champion, 2016 Wimbledon finalist, 2018 Australian Open semifinalist.

4. Naomi Osaka
Slam Index: 4,292.5
Slam Quarterfinals made over span: 2
Best Slam results over span: 2019 Australian Open Champion, 2018 US Open Champion.

5. Karolina Pliskova
Slam Index: 3,305.0
Slam Quarterfinals made over span: 7
Best Slam results over span: 2016 US Open finalist, 2019 Australian Open semifinalist, 2017 Roland Garros semifinalist

6. Madison Keys
Slam Index: 3290.0
Slam Quarterfinals made over span: 5
Best Slam results over span: 2017 US Open finalist, 2018 US Open semifinalist, 2018 Roland Garros semifinalist

7. Garbiñe Muguruza
Slam Index: 3,255.0
Slam Quarterfinals made over span: 4
Best Slam results over span: 2017 Wimbledon Champion, 2016 Roland Garros Champion, 2018 Roland Garros semifinalist.

8. Ashleigh Barty
Slam Index: 3,242.5
Slam Quarterfinals made over span: 2
Best Slam results over span: 2019 Roland Garros Champion.

9. Sloane Stephens
Slam Index: 3,185.0
Slam Quarterfinals made over span: 4
Best Slam results over span: 2017 US Open Champion, 2018 Roland Garros finalist.

10. Caroline Wozniacki
Slam Index: 2,690.0
Slam Quarterfinals made over span: 3
Best Slam results over span: 2018 Australian Open champion, 2016 US Open semifinalist.