Is Serena Williams' Hold on the WTA's No. 1 Ranking Suddenly in Danger?

Serena Williams has held the No. 1 ranking on the WTA Tour for 163 consecutive weeks. She's been so dominant over the past three years that even after a loss, her reign at the top never seemed in doubt, until now.  

A surging Victoria Azarenka and surprisingly consistent Angelique Kerber pose a serious threat to Williams' No. 1 ranking.

Williams leads the WTA field with 9,505 points. She'll lose 880 of those points after failing to defend her title in Miami. 

When the new rankings come out on Monday, Azarenka will be back in the Top 5 for the first time since May 2014. Kerber will return to No. 2 and be within 2,600 points of Williams.

The points' math is stacked against Williams, and the pressure is on. 

After losing to Roberta Vinci in the semifinals of the 2015 U.S. Open, Williams had 11,500 points and nearly a 6,000-point lead over then-No. 2 Simona Halep.

But after shutting down her season early and failing to defend titles at the WTA Tour Championships, the Australian Open and Miami, Williams is suddenly vulnerable.

She heads into the clay-court season with 4,000 points to defend at the French Open and Wimbledon. 

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Meanwhile, because she struggled last year, Azarenka has fewer than 1,000 points to defend between now and Wimbledon. Early exits by Williams and title wins from Azarenka could put Vika in position to get back on top by the end of this year. 

Although Kerber has to defend titles at Charleston and Stuttgart, last year she lost in the third round at Roland Garros, Wimbledon and the U.S. Open. With more favorable draws, Kerber could make a run at points in the last three Slams. 

Williams' best chance to make up ground comes in Rome, where she did not play last year. At stake is a chance to best Steffi Graf (186) for most consecutive weeks at No. 1.

Azarenka began the year with just 2,276 points. Kerber had only 3,590. Williams, even after ending her season early, started with 9,545. She's already lost 1,320 points this season. 

Previously, Azarenka struggled to close out Williams. 

After her win at Indian Wells, Azarenka told reporters (via Tennis.com) she believes she's playing better than she was when she was No. 1. 

 “I can move the way I want to move, and (I) see improvements in my game. This is what keeps me excited, keeps me motivated, and seeing that it works against the best player in the world just brings a little bit extra to work even harder."

Although Williams is not finishing off opponents in her usual winning fashion, she's also not crashing out against low-ranked players. Her last four losses have come to players who went on to either reach the final or win the tournament.

The problem for Williams is the quest to remain No. 1 is probably secondary to winning another Grand Slam. More Slams can cement her claim to greatest of all time. 

However, the race for No. 1 is not about who is the greatest player ever. It's a points system that rewards players for what they've done lately and punishes those who fail to back up wins. The bigger your year, the harder the potential fall.  

That's why we see Eugenie Bouchard, who reached a career-high No. 5 in the fall of 2014, languishing at No. 45. 

Williams will fall to No. 3 in this year's Road to Singapore points race. Either Kerber or Azarenka will finish No. 1, pending the outcome of the Miami Open final. 

After her loss in Miami, Williams gave a brief press conference. When asked about her movement and what went wrong, Williams told reporters (via ASAP sports transcripts), "I did the best that I could. My fans, you know, I did the best I could do. I can't win every match. The players come out and play me like they've never played before in their lives. ... You know, the best that I could do today. I have to be 300 percent every day, so..."

When you're out in front, there's always a target on your back. But now Kerber and Azarenka are within reach. Williams can expect them to push hard, especially now that they know they can beat her.