Ana Ivanovic is out of the US Open in the first round for the second straight year after a 7-6 (7-4) 6-1 loss to Denisa Allertova of the Czech Republic.
Ivanovic is a former No.1 player and 2008 French Open winner who has slipped to No.31 in the rankings.
The Serb was serving for the first set at 6-5 on Tuesday but struggled with her serve and faltered in the tiebreaker. She finished with seven double-faults and 41 unforced errors.
At the Open, she has reached the fourth round or better five times, including a career-best quarter-final run in 2012.
The 89th-ranked Allertova improved to 7-1 in first-round matches in majors, making her second main-draw appearance at the Open.
Earlier, fifth seed Simona Halep blasted her way into the second round by demolishing Kirsten Flipkens 6-0 6-2 and underlining her credentials as a potential grand slam winner.
Halep, a winner of three WTA Tour events this season, carried her superb form into Flushing Meadows as she needed just one hour on a sun-splashed but almost vacant Arthur Ashe Stadium court to dismiss the 56th-ranked Belgian.
Flipkens, a former grand slam semi-finalist who advanced to the last 16 at the Rio Olympics, look headed to a humiliating double bagel as Halep swept through the opening 11 games.
But with Halep serving for the match Flipkens broke her Romanian opponent before thrusting her arms into the air in mock triumph.
Flipkens would then hold serve for the first time but her late bit of resistance only prolonged the inevitable as Halep closed out the rout to setting up a second-round meeting with Czech Lucie Safarova.