New York - Serena Williams once again arrives at Flushing Meadows poised to rewrite the tennis record books -- if her own troublesome right shoulder and increasingly emboldened rivals allow.
The 34-year-old US superstar matched Steffi Graf's Open Era record of 22 Grand Slam singles titles with her triumph at Wimbledon in July.
With a seventh US Open triumph she can break Graf's record, and continue her march toward Australian Margaret Court's all-time mark of 24 Grand Slam titles.
She could also break Graf's record of 186 consecutive weeks atop the world rankings, and surpass Chris Evert for most US Open singles titles won in the Open Era.
But after seeing a frustrating year go by between her 21st Grand Slam win and No. 22, Williams said she'd learned to let history take care of itself.
"At this point, I'm taking it a day at a time," Williams said. "I just am more relaxed, for sure."
A straight-sets win over Angelique Kerber in the Wimbledon final may have eased some of the pressure Williams was feeling, but it's been far from smooth sailing since.
Her bid to retain her Olympic singles title ended in Rio de Janeiro when she was sent crashing out of the third round by Elina Svitolina.
Williams was clearly hindered by the shoulder injury that had forced her out of the Montreal WTA tournament as she served up eight double faults and 37 unforced errors in the straight-sets defeat.
She then withdrew from her WTA title defence in Cincinnati, still struggling with painful shoulder inflammation.
"I think usually I prefer to play more coming into the final Grand Slam of the year," Williams acknowledged. "But there is nothing we can do about it. You just have to make the best of every single opportunity. That's all I can do now."
Williams faces a tricky opening encounter against experienced Russian Ekaterina Makarova.
Germany's Kerber, who defeated Williams in the Australian Open final in January, is just one of the players with a chance to seize the number one ranking if Williams falters.
Kerber, 28, also boasts a title at Stuttgart, an Olympic silver medal and finals appearances at Brisbane in January and this month in Cincinnati -- where she missed her first chance to supplant Williams atop the rankings.
Being viewed as a legitimate threat to Williams, Kerber said, "is really special".
"Because Serena is one of the best players and athletes in the world," she said.
Far from feeling stressed by the chance to topple Williams, Kerber said she is thriving on the race for number one.
"I love this question, I love it," Kerber said. "The pressure for sure is maybe a little bit higher, but if I'm not doing the pressure on myself, everything is fine."
Third-seeded Spaniard Garbine Muguruza also has a shot at the top, although the 22-year-old who stunned Williams in the French Open final will need her best US Open ever to do so.
In three main-draw appearances she has won just one match. Turning around her Flushing Meadows fortunes would further her aim of establishing herself as more than "the girl that beat Serena" at Roland Garros.
Fourth-seeded Agnieszka Radwanska of Poland also has an outside chance at the world number one ranking if she can claim her first Grand Slam title.
Notable absentees include 2015 champion Flavia Pennetta, who retired at the end of last year, Victoria Azarenka who is pregnant and former champion Maria Sharapova who is serving a doping suspension.
Venus Williams, whose seven Grand Slam titles include two US Opens, is among a handful of former champions among the seeds including 2004 winner Svetlana Kuznetsova of Russia and 2011 champ Samantha Stosur of Australia.
"There are a lot of good players right now," Kerber said. "Let's see how Serena will play here. Let's see how the others will play. It's a new day, new tournament, new matches -- so let's see."