Simona Halep vowed to "move on fast" from a shock first-round defeat to Kaia Kanepi at the US Open.

The world number one was among the favourites to win a first title at Flushing Meadows, but was beaten 6-2 6-4 by 33-year-old Estonian Kanepi on day one.

Halep was no match for an inspired world number 44, who reached the quarter-finals last year and looked capable of a repeat as she brushed the top seed aside on the first match in the new Louis Armstrong Stadium.

The French Open champion came into the final major of the year in great form, having won the Rogers Cup and lost to Kiki Bertens in the Cincinnati Masters final before skipping the Connecticut Open last week.

Halep said a hectic schedule had taken its toll, but did not use that as an excuse for her second consecutive first-round exit in New York.

Asked about the scheduling before the US Open, Halep said: "I don't blame that. It just was a bad day. And I never play my best tennis here, even if I did quarter-finals, semi-finals.

"I feel like my game is not...at the best level [in New York, but I have always fought for every match. I did today, but it didn't go my way."

Halep insisted she will have no problem picking herself up after a surprise setback.

"After the Cincinnati final was not that easy. Today it's easier, because I really couldn't play my best game because of many reasons; stressed a little bit, emotions. You cannot control everything all the time," she added.

"It is easier, actually, after winning a grand slam, the pressure is off. I'm trying just to relax more, but it's always tough to lose a match, because I'm very competitive player. 

"It's tough to lose. Sometimes I have tears, it's normal. But now I feel better. I feel that it just was a bad day, and I will move on fast."