US Open 2015: Heather Watson rues missed chance at US Open

Heather Watson has not won a match in the US Open main draw

British number one Heather Watson said she let the tension get to her as she lost to world number 84 Lauren Davis in straight sets at the US Open.

American Davis won 7-6 (7-3) 7-6 (7-0), condemning Watson to a fifth straight first-round defeat in New York.

The Briton, ranked 61st, had previously been drawn against the likes of Maria Sharapova, Li Na and Simona Halep.

"I'm very disappointed with the loss. I thought it was an opportunity but it's never easy," Watson told BBC Sport.

"I think all matches at Grand Slams are tough and everybody raises their level. But it's done now - I can't go back and change it."

Watson, 23, earned the first three break points of the match in game six, and would later serve for the second set, but could not find her game consistently enough.

Davis, 21, dominated both tie-breaks to claim her first win in four attempts at Flushing Meadows.

"I thought too much about winning rather than the process and trying to play the right way, using the game plan that I prepared before the match," said Watson.

"It was tough conditions and I wasn't able to do that."

The match was scheduled first on court 17 at 11am local time but the temperature was soon approaching 30C, and Watson suffered with cramp in her hand.

"I don't think that was due to my fitness," she said.

"It was more down to me being tense in the beginning of the match, but that's just something I have to deal with. It didn't stop me too much. She played well to win the match."

Watson still has to play doubles with New Zealand's Marina Erakovic, but will then move on to Asia in the search of enough ranking points to get back in the world's top 50.

"I still have the opportunity every week I play to do well. It's a real shame, this being a tournament that I like and enjoy coming to.

"There was a lot to gain here, but I've just got to think ahead to the next week now."