Women's tennis remains in a state of flux, as the leading exponents of the game prepare for the final Grand Slam tournament of the season in New York.
Simona Halep is the rightful No 1 at present, after six months atop the WTA standings, but it wouldn't take too many surprise results to switch things around fairly quickly.
The last seven slams have been claimed by as many different players, which is a rarity in the modern era.
And if this year's US Open is not won by Caroline Wozniacki, Halep or Angelique Kerber then, for the second season in a row, the four big titles will have been shared around.
The Main Challengers
Kiki Bertens: One of the most improved players of 2018. She reached the quarter-finals at Wimbledon and beat four top-eight ranked players en route to taking the title in Cincinnati. This was her second WTA Tour title on American soil this year.
Simona Halep: A deserving world No 1 after claiming a maiden Slam title at Roland Garros in June. The 18-time Slam winner Martina Navratilova recently said Halep finally looks like a true No 1 and since losing on grass at Wimbledon has played well on the hard courts of North America. She won the Rogers Cup in Montreal before losing in the final at Cincinnati, where she briefly held a match point in the second set tie-break against Kiki Bertens. The only doubt for Halep is that she withdrew from this week's event in the US citing an Achilles problem. Hopefully, for the 26-year-old Romanian, this was just a precautionary measure.
Daria Kasatkina: Made it through to the last eight at Roland Garros and Wimbledon, while also losing two finals earlier in the year. Although an unlikely champion in NY, the 21-year-old Russian has reached a career-high No 11 in the world rankings.
Angelique Kerber: The three-time Slam champion from Germany fears no one. Kerber won in New York two years ago and has beaten Serena in two of their three Grand Slam final showdowns. The 30-year-old has reached the last eight of all three Slams during 2018, winning at Wimbledon last month.
Petra Kvitova: A winner of five titles this season, all during the first half of the year. Has twice been a quarter-finalist at the US Open.
Garbine Muguruza: The two-time Slam winner has never been the most consistent of players despite having the talent and athletic ability to be a potential world No 1. She is yet to reach the semi-finals of a hard court slam but can't be ruled out either.
Sloane Stephens: Looks like the real deal after many years travelling up and down the world ranking. The 25-year-old is the defending champion but is prone to some serious slumps in form. Runner-up to Halep in Paris, the American then suffered a shock first round defeat at SW19 where she won just four games. Since then, however, she has reached the final in Montreal losing in three sets to Halep.
Serena Williams: Don't let her first and second round defeats in San Jose and Cincinnati respectively, fool you into thinking Serena is struggling right now. The 36-year-old only seems interested in Slams nowadays, as she searches for that one more title that will bring her level with Margaret Court who holds the all-time record of 24 career victories. The American remains a threat and will only get stronger the longer she stays in the tournament. Her biggest worry is surviving the early rounds. However, the last time she failed to reach the semi-finals at Flushing Meadows was in 2007. She missed last year's instalment due to the pending birth of her first child.
Caroline Wozniacki: Has struggled to follow-up her early season success in Melbourne which briefly took her to No 1 in the world ranking. The Dane is a two-time runner-up at Flushing Meadows.
CLICK THE LINK BELOW TO VIEW FORM AT LAST 10 GRAND SLAM EVENTS
Twitter: Andy Swales@GolfStatsAlive