4) Garbine Muguruza
Ever since World Number 3,Spaniard Muguruza won the French Open this year she has failed to show fine form in the Grand Slams. She succumbed to second round losses in both Wimbledon and again at the US Open.
With an all total of 38 unforced errors from her side, each shot increasingly worse in quality, she made the job easy for 48th ranked Latvian Anastasija Sevastova. Muguruza has been struggling to find her form and in that match, she looked lost and fired randomly to make shock-exit 7-5,6-4.
The Parisian clay courts of Roland Garros which had been friendly to the 22-year old Muguruza was the only last happy memory she has of Grand Slam success. The US Open had always been out of her reach, as she never was able to make it past the first few rounds. Being the World Number 3, it is only necessary for her to buck up and pick her falling game if she has any desire at all to hold on to the Number 3 spot on the WTA rankings.