World number one Simona Halep has been knocked out of the US Open.
The Romanian lost 6-2 6-4 to Kaia Kanepi who is ranked No. 44 in the world.
Halep’s serve was broken five times as she fell to a shock defeat in the first match at the rebuilt Louis Armstrong Stadium at Flushing Meadows.
Top-ranked Halep fought back from a double break down to 4-4 in the second set but the Estonian broke again before the 26-year-old sent a forehand long on match point.
Halep is the first top-seeded woman to lose in the first round in New York. She also becomes the sixth No. 1-seeded woman to lose in the first round of a Grand Slam in the Open era. Angelique Kerber lost as a No. 1 seed in the first round of the 2017 French Open.
At Roland Garros in late May, Halep ceded the opening set of her first-round match by that same score against 83rd-ranked Alison Riske, before coming back to win that match 2-6, 6-1, 6-1, to claim her first major championship.
Recall Halep also lost in the first round at last year’s U.S. Open to 2006 champion Maria Sharapova.