NEW YORK (AP) -- At first glance, this U.S. Open might appear as unpredictable as any.
From recent injuries to players such as Serena Williams, Naomi Osaka and Simona Halep, to a bit of pre-tournament shakiness from Roger Federer and Novak Djokovic, to Rafael Nadal's issues on hard courts, to the group of up-and-coming men's issues at Wimbledon, it's difficult to predict what will unfold at Flushing Meadows over the next two weeks.
And yet this much is clear with main-draw action set to start Monday: If they're healthy, then the expected champions will come from a small group of women that includes Williams, Osaka and Halep and the members of the men's Big Three.
"It seems like the same guys are the favorites again this time around," said Federer, who won five of his men's-record 20 Grand Slam singles championships at the U.S. Open, although the last came in 2008. "It will be a surprise if anybody else won."
Williams has won six of her 23 major singles trophies in New York, most recently in 2014. Since then, she lost in the semifinals twice, missed the 2017 edition because she gave birth and was the runner-up a year ago to Osaka in a match that stood out more for Williams' conflict with chair umpire Carlos Ramos than the tennis itself.
The key for the 37-year-old American, as it's been throughout her return since having a daughter, is her health and fitness, because her serve and other strokes are capable of being just about as dominant as ever. Williams reached the final at three of the past five Grand Slam tournaments; she lost each time, leaving her still just one major singles title away from equaling Margaret Court for the most in the sport's history.
"The years are passing, and she's not getting any younger," said 1994 Wimbledon champion Conchita Martinez, who coaches 2016 U.S. Open runner-up Karolina Pliskova. "But she has a shot."
Probably only if her back is fine, though. Williams stopped playing in the final of the Rogers Cup hard-court tuneup this month after having back spasms, then cited that same problem when she pulled out of the following week's tournament.
Williams has withdrawn or retired from all of her non-Slam events in 2019. Unlike other top players, she didn't hold a pre-tournament news conference at the U.S. Open, but both Osaka (left knee) and Halep (left Achilles) declared themselves OK.
Djokovic did the same after having a trainer check on blisters on his right foot while he practiced Saturday. He and Federer went a combined 4-2 in hard-court matches after their historic five-set Wimbledon final. Nadal, meanwhile, has a long history of injury setbacks on a surface that is unforgiving, including retiring from his U.S. Open semifinal last year.
Still, there's a reason one needs to go all the way back to Andre Agassi in 2003 to find someone other than Djokovic, Federer or Nadal seeded No. 1 in New York.
Here is what to know as the U.S. Open starts:
BIG 3 STILL BIG
Djokovic, Nadal, and Federer have combined to take 11 Slam titles in a row and 54 of the past 65. One thing to keep an eye on: Federer and Nadal have played each other 40 times but never at the U.S. Open. It could only happen if both reach the Sept. 8 final.
COCO IS BACK
Coco Gauff appears in her second major after her captivating run to Wimbledon's Week 2 as a qualifier ranked just 313th. The 15-year-old, who is based in Florida, was granted a wild card by the U.S. Tennis Association into singles and doubles (with Caty McNally, a 17-year-old from Ohio).
KYRGIOS ON DISPLAY
In reaction to what went on in last year's Williams-Osaka final, the USTA will post code violations -- racket abuse, say, or unsportsmanlike conduct -- on scoreboards. That might be put to use Tuesday, when 28th-seeded Nick Kyrgios plays Steve Johnson. Kyrgios was fined more than $100,000 for his tantrums during a recent match, hardly his first such sanction. "You've just really got to focus on what you're trying to accomplish, your game plan," Johnson said. "He's going to do what he's going to do."
ARE THE KIDS ALL RIGHT?
The tennis world has been waiting for a younger player to challenge the top men. Three guys pegged for that sort of success -- Dominic Thiem, Alexander Zverev and Stefanos Tsitsipas -- all lost in the first round at Wimbledon. How will they rebound at the U.S. Open? Someone else to track: Daniil Medvedev, a 23-year-old Russian whose best Slam showing was a fourth-round appearance at the Australian Open in January. He has been to the finals at three consecutive hard-court tournaments.
