Serena Williams can lose her No. 1 ranking to 3 women at the US Open

Serena Williams has been the most dominant player in women’s tennis for years, and has legitimate claim to the title of greatest ever. But for the first time in over 180 weeks, she could lose her No. 1 ranking in the world if the US Open doesn’t go her way.

The final Grand Slam of 2016, the US Open features stiff competition in Angelique Kerber, Garbine Muguruza and Agnieszka Radwanska, in addition to the slew of other competitors who are all hoping for upsets.

Williams has handled all of this competition and then some in the past, but her recent play has been spotty as she has struggled to consistently win her finals and hold off her top-seeded opponents. She was eliminated within the first three rounds of the Summer Olympics -- in both singles and doubles play -- and lost in the finals of both the Australian Open and French Open earlier in the year.

Williams, 34, has 22 Grand Slam singles titles to her name, putting her in a tie with Steffi Graf for most by any woman in the Open Era. It’s likely that Williams will pass that mark, and in the near future, but she seems more vulnerable now than ever.

Kerber has the best shot of unseating Williams. She is defending just 130 points at the US Open after losing in the third round last year. Williams is defending a 780 from her 2015 run. Even if Kerber loses in the first round of the tournament, Williams will still have to at least make the semifinals to hang on to her No. 1 ranking. If Kerber makes it to the quarterfinals, Williams would need to make the final. If Kerber makes the final, then Williams has to beat her there.

In a way, Williams is chasing Kerber rather than vice versa.

Muguruza has the next best chance, though her way forward isn’t as simple as Kerber’s. She has to make it to at least the semifinals, and she needs Williams to fall before the quarterfinals. Keep in mind, Muguruza has only ever won a single match at the US Open and Williams hasn’t been out before the quarterfinals since 2006.

If Muguruza were to make it to the semifinals and then she faced Kerber, she would have to beat Kerber there and win in the finals to get the ranking. If Williams fails to make the semifinals and Muguruza makes the final, she passes Williams. It’s even possible that both Muguruza and Kerber end up ahead of Williams.

Finally, Radwanska can earn the No. 1 ranking. She would need to win the tournament, and she would need Kerber to lose before the finals. She could face Williams in the semifinals, though she has never beaten Williams in head-to-head action. If Radwanska were to face Muguruza in the finals and she won, then Williams could fall all the way to fourth in the world.

Williams isn’t playing terrible tennis by any means. She won in the finals at Wimbledon and made both Grand Slam finals earlier in the year, even if she lost them. She has played just three matches since winning Wimbledon, though, while her chief competition has been active and relatively successful.

You should never bet against Williams, not until she has well and truly called it a career. That day is long off yet, but her No. 1 ranking can still fall. Few expected Kerber to experience a career resurgence and play the best tennis she’s ever had as she approaches the age of 30, and nobody guessed Muguruza would have the resolve to take down Williams at the French Open.

Anything can happen when the US Open gets underway on Monday. But if Kerber, Muguruza or even Radwanska want Williams’ top spot, they’re going to have to take it.