Simona Halep became the first top-seeded woman to lose in the first round of the U.S. Open in the open era by losing 6-2, 6-4 to No. 44 Kaia Kanepi.
The defeat marked the second-straight year in which Halep lost in the opening round of the U.S. Open. She lost last year as the No. 2 seed to Maria Sharapova. Halep won her first major at the French Open in 2018.
The Romanian entered the U.S. Open on a hot streak by winning the Rogers Cup on Aug. 8 and finishing second in the Cincinnati Masters on Aug. 19. She struggled throughout Monday's match with Kanepi and coughed up 28 unforced errors.
Kanepi advanced to 19–10 in her career at the U.S. Open on Monday. She reached the quarterfinals in 2017.