Heather Watson admits nerves got the better of her as the British No.1 lost to America's Lauren Davis in the US Open first round on Monday.
Watson was hoping to progress to round two at Flushing Meadows for the first time in five attempts but it was Davis who claimed two tiebreaks to go through 7-6(3), 7-6(0).
The defeat was a heavy blow for Watson, who won the junior title in New York in 2009, but is yet to win in the senior competition, previously falling victim to distinguished opponents including Maria Sharapova, Li Na and Simona Halep.
Watson had said before the tournament that she was interested in a rematch with Serena Williams after their memorable Wimbledon clash, but she admitted after her latest disappointment that she had struggled physically and mentally in New York.
"I was thinking a lot about this match, thinking that it was a big opportunity, and thinking about the previous years and my results here," Watson said.
"Maybe I thought about that a bit too much. I was cramping a little bit in my hand, and then when I moved to the other side of the court I started cramping in my legs.
"I'm fit coming into the tournament. It's not that I'm not fit. It was just a mix of the tension and a bit of the stress and everything together."
Watson has been eager this year to add aggression to her speed, tenacity and strong defensive play but made too many mistakes from the baseline and got her tactics wrong.
"I should have come into the net a lot more than I did," Watson said. "That goes back to playing a bit tense and defensive.
"I won most of the points I did come to the net, and I should have done it more. I didn't execute my game plan the way I wanted to."
Watson will play in the doubles with New Zealander Marina Erakovic before returning to London ahead of four weeks in Asia. It leaves Laura Robson and Johanna Konta as Britain's representation in the women's draw, with both players in action on Tuesday.
Robson continues her comeback from injury against Russian Elena Vesnina while Konta, who came through qualifying, is looking to extend a 13-match winning streak against American wildcard Louisa Chirico.