NEW YORK, NY, USA – Garbiñe Muguruza’s shock exit to Anastasija Sevastova whittled down the number of contestants in the US Open’s No.1 ranking sideshow to three: Serena Williams, Angelique Kerber and Agnieszka Radwanska.

As the tournament enters its opening weekend wtatennis.com updates the state of play in the race for top spot…

Serena Stays On Course: Williams entered the US Open as the World No.1, a distinction she has held since February 18, 2013. Through the two weeks of the US Open, Williams will extend her streak to 186 consecutive weeks, tying the WTA record for most consecutive weeks at No.1 held by Steffi Graf (August 17, 1987-March 10, 1991).

Williams’ reign is all the more remarkable considering the 186 weeks preceding her ascension saw the No.1 ranking change hands nine times, with Dinara Safina, Serena, Caroline Wozniacki, Kim Clijsters, Victoria Azarenka and Maria Sharapova all spending time at the summit.

In the opening two rounds, Williams has answered the questions regarding the health of her troublesome shoulder with business-like wins over Ekaterina Makarova and Vania King. To extend her current stint as No.1, Williams, who is defending 780 points, will need to at least reach the semifinals.

The longer Kerber stays in the tournament, though, the further Williams will need to advance:

– If Kerber reaches the quarterfinals, then Williams must reach the final.
– If Kerber falls in the semifinals, Williams would remain at No.1 by reaching the final.
– A championship match showdown between Williams and Kerber would see the winner walk away not only with the trophy, but the No.1 ranking.

Williams’ ranking points have come from seven tournaments in the last 52 weeks – 2015 US Open (780), Australian Open (1300), Indian Wells (650), Miami (120), Rome (900), Roland Garros (1300) and Wimbledon (2000).

What Will It Take For Kerber To Become World No.1?: Kerber is bidding to become the 22nd player to reach No.1 since the computer rankings were introduced in November 1975. In her previous tournament, the German came within one win of unseating Williams at No.1 in Cincinnati, only to fall short in the final against an on-song Karolina Pliskova.

The disappointment does not appear to have lingered, making short work of her opening two opponents, Polona Hercog and Mirjana Lucic-Baroni.  Last year, Kerber lost to Victoria Azarenka in the third round at the US Open and as a result is only defending 130 points in Flushing Meadows. Kerber will have a 460-point advantage from the start of the tournament, therefore even a surprise third-round loss to crowd favorite CiCi Bellis does not rule her out of contention.

Kerber consistently has reached the business end of the WTA’s biggest events with six finals appearances this year, winning the titles at the Australian Open and Stuttgart, finishing as runner-up at Brisbane, Wimbledon, Cincinnati and the Olympics*. As a result, Kerber’s ranking has been on a steady incline after finishing 2015 at No.10.

* There were no ranking points awarded for this year’s Olympic tennis competition.

US Open Title Could Vault Radwanska To Top Spot: Agnieszka Radwanska will need to win the US Open title, to have reach the top spot. However, if Kerber reaches the final, Radwanska could only move as high as No.2.

The Pole came through her first test in the second round, surviving an epic opening set tie-break to eventually defuse the big-serving Naomi Broady. Next up is the gifted, if unpredictable, Caroline Garcia