Serena Williams has been seeded 17th at this year's US Open one place below her sister Venus, organizers said on Tuesday.
Serena, who finished runner-up at Wimbledon this year after losing to Germany's Angelique Kerber in the final, is ranked 26th in the world, nine places below the seeding she has been awarded.
The current WTA rankings are the usual criteria to decide seeding in the women's draw.
Williams, who has won the U.S. Open six times and will turn 37 next month, missed last year's tournament because of pregnancy.
In June, United States Tennis Association president Katrina Adams said the U.S. Open would revise seedings to take into account the effect of pregnancy on the current rankings of players.
Adams' comments came in the wake of widespread criticism of tennis officials after Serena was denied a seeding at this year's French Open, her first grand slam after returning to the sport.
Romanian Simona Halep is the top seed in the women's draw with defending champion Sloane Stephens at number three, ahead of Kerber, who won at Flushing Meadows in 2016.
There were no surprises on the men's side with world number one and defending champion Rafa Nadal named top seed, ahead of Roger Federer and Argentine Juan Martin del Porto in third.
Wimbledon champion Novak Djokovic, who heads to Flushing Meadows in arguably his best form since returning from a troublesome elbow injury, is seeded sixth, a place below big-serving South African Kevin Anderson.
John Isner is the highest-seeded American in the men's draw at number 11.