U.S. Open 2018: Top seed Simona Halep upset by Kaia Kanepi

Simona Halep (Getty Images)

Kaia Kanepi pulled off a major upset on day one of the U.S. Open with a straight-sets defeat of world No. 1 Simona Halep.

Halep was blown away by the 33-year-old Estonian in the first match at the new Louis Armstrong Stadium, losing 6-2, 6-4 on a warm Monday in New York.

The composed 44th-ranked Kanepi outplayed the top seed with a mixture of power and precision to send shock waves around Flushing Meadows.

Halep was beaten by Maria Sharapova in the opening round at the final major of the year 12 months ago and, although the French Open champion showed some fight in the second set, the previously in-form Romanian was unable to avoid becoming the first top-seeded woman to lose in the first round of the tournament.

The unseeded Kanepi reached the quarterfinals of the U.S. Open last year and will face Jil Teichmann in round two after breaking five times and hitting 26 winners in an aggressive performance to claim a huge scalp.