Power Rankings: Halep joins Serena in top two; Pliskova, Suarez Navarro rise

Welcome to SI Tennis Power Rankings – a recurring feature on SI.com that goes beyond the regular ATP and WTA rankings to grade and rank the top 20 men's and women's players by more than just points earned on tour, including everything from injuries and meltdowns to big upsets and recent title wins, as well as other subjective assessments.

Welcome to SI Tennis Power Rankings – a new recurring feature on SI.com that goes beyond the regular ATP and WTA rankings to grade and rank the top 20 men's and women's players by more than just points earned on tour. While tournament results and quality of play are considered, SI Tennis’ Power Rankings also take into account those unquantifiable metrics that make the sport so compelling—everything from injuries and meltdowns to big upsets and recent title wins, as well as other subjective assessments. Each edition of SI Tennis Power Rankings is intended to capture a more seasonal and timely portrait of the current tennis rankings.

Check out the newest edition of SI Tennis Power Rankings below. 

1. Serena Williams

Previous Power Ranking: 1

Serena is still undefeated to start the year, winning her 19th major at the Australian Open and eighth Miami Open title. Her much-hyped return to Indian Wells ended prematurely due to a knee injury, but Serena hasn't taken a wrong step so far in 2015. 

2. Simona Halep

Previous Power Ranking: 3

For a player that struggles at times with self-belief, Halep has a remarkable knack of forging new ground. She's already won three titles, including the biggest one of her career at Indian Wells. She followed that up with a career-best run in Miami, narrowly losing to Serena in the semifinals. Now we move to her best surface: clay. 

3. Maria Sharapova

Previous Power Ranking: 2

After a great January with wins in Brisbane and a run to the Aussie final, Sharapova lost her mojo in North America. A stomach illness forced her out of Acapulco and she suffered early losses to Flavia Pennetta and No. 97 Daria Gavrilova in Indian Wells and Miami, respectively. That she appeared to be nursing a leg injury in Miami is worrisome as she tries to defend a big chunk of points on clay.  

4. Karolina pliskova

Previous Power Ranking: 12

No one outside of the Top 5 has been as consistently impressive as the young Czech. She flew from Australia to Canada and won both of her Fed Cup singles matches, then traveled to Antwerp and made the semifinals, followed by a trip to the Middle East to make the Dubai final. Finally, she returned back to the U.S. to make the fourth round or better at both Indian Wells and Miami. 

5. Venus Williams

Previous Power Ranking: 5

Venus scored two good wins—one over Agnieszka Radwanska in Dubai to make the semifinals and one over Wozniacki in Miami to make the quarterfinals. The eye-ball test says she's not playing with the same spark as she did to start the season, but losses to a resurgent Victoria Azarenka and Carla Suarez Navarro shouldn't sound any panic alarms.

6. Carla suarez navarro

Previous Power Ranking: Out of Top 20

The Spaniard made her Top 10 debut this week and is actually No. 4 in the WTA Race rankings. Her consistency has led to her best start to any season, making the quarterfinals or better at seven of her eight tournaments. But she has yet to prove she has a game that can bother the WTA's very best. 

7. Timea Bacsinszky 

Previous Power Ranking: Out of Top 20

Bacsinszky has lost just one match since the Australian Open. She won back-to-back titles in Acapulco and Monterrey and then lost to Serena in the fourth round of Indian Wells before pulling out of Miami to rest. All the while she's been using her platform to shine a light on physically and emotionally abusive tennis parents, speaking openly about how the sport destroyed her family. That's courageous stuff both on and off the court. 

8. Andrea petkovic

Previous Power Ranking: Out of Top 20

Petkovic did well to take the pressure off her upcoming clay season, where she's defending a lot of points. She won the title in Antwerp, came up huge for Germany in Fed Cup and made the Miami semifinals. Not bad for someone who started the season 0-3. 

9. Victoria azarenka

Previous Power Ranking: 14

The former No. 1 has played just three tournaments since the Australian Open but she's impressed with her improved form. She made the Doha final with wins over Angelique Kerber, Wozniacki and Venus. Her North American swing didn't go as well as she wanted but given her progressing health and fitness, she's a firm threat to make the final of any tournament she enters.  

10. Caroline wozniacki

Previous Power Ranking: 8

Wozniacki's losses this year have come to a small group of talented champions like Venus (twice) and Azarenka (twice). But this is still a disappointing start to the season for Wozniacki, who ended 2014 on an absolute roll.  

11. Ekaterina makarova

WTA Ranking: 8
Previous Power Ranking: 9 

After making the Australian Open semifinals, Makarova has not beaten a Top 25 player.

12. Madison Keys

Previous Power Ranking: 10

The 20-year-old is still a work in progress. She's won one match since her breakout run at the Australian Open, but they've been to quality players in Jelena Jankovic and Sloane Stephens. Tough, but not bad losses. 

13. Lucie Safarova

Previous Power Ranking: Out of Top 20

February was a good month for Safarova. She made back-to-back quarterfinals in Antwerp and Dubai (losing to Pliskova both times) and then won the biggest title of her career in Doha. That run cost her in North America though, where she won just one match. 

14. Garbine Muguruza

Previous Power Ranking: 15

Muguruza followed up her fourth round run in Melbourne with a big win over Halep in Romania for Fed Cup and a semifinal in Dubai. But she hasn't been the same since coming down with a viral illness in Doha. One big takeaway from her season so far: Pliskova vs. Muguruza is a young rivalry to watch. Their matches are great.

15. Jelena Jankovic

Previous Power Ranking: Out of Top 20

It's hard to know how much to read into Jankovic's run to the Indian Wells final, which she probably should have won given that she served for the match. But as she moves onto clay, she's put herself back into the conversation. 

16. Caroline Garcia

Previous Power Ranking: Out of Top 20

Overshadowed by Bacsinszky's back-to-back titles in Mexico was Garcia's back-to-back finals. That's some good consistency from the erratic but talented Frenchwoman. She was also the Fed Cup hero for France in their big upset over Italy. 

17. Sabine lisicki

Previous Power Ranking: Out of Top 20

The German's decision to bring in former ATP player Christopher Kas as coach is paying off. After going 1-6 to start the season, Lisicki was a revelation in the U.S., making the semifinals in Indian Wells and taking Serena to three sets in the Miami quarterfinals. 

18. Petra Kvitova

Previous Power Ranking: 4

The Czech is in a holding pattern. After back-to-back losses to Suarez Navarro in the Middle East, Kvitova pulled out of the North American swing due to exhaustion. 

19. Agnieszka radwanska​

Previous Power Ranking: 6

The Pole is slumping and, at her lowest ranking since 2011, on the verge of dropping out of the Top 10.

20. Ana Ivanovic

Previous Power Ranking: 7

Despite making the Brisbane final to start the year., Ivanovic hasn't beaten a Top 25 player all season. That she continues to play on an injured foot doesn't inspire much confidence in a quick turnaround.