Heather Watson admitted last night that the stress of the occasion had got to her as her winless US Open streak continued with a 7-6, 7-6 defeat by the American, Lauren Davis.

The 23-year-old has now lost in the first round here for five consecutive years and despite winning the junior title in 2009, she has yet to win a senior match at Flushing Meadows, including one in qualifying.

Three of those losses came to Maria Sharapova, Simona Halep and Li Na but Watson’s performance yesterday was a far cry from Wimbledon, where she was within two points of beating Serena Williams in the third round. On a couple of occasions, the world No.61 looked to be in physical difficulties, perhaps a result of a golden opportunity slipping away.

“Maybe it was just a mix of tension and some long rallies mixed together,” she said, trying to piece together the reason for the defeat. “I didn't feel…I was sweating a lot. I don't know. I found it quite hot today. I felt fine before the match. I was hydrated. I had been drinking a lot the days before and eating the right things and got an early night and I slept fine.

“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. I think that maybe I thought about that a bit too much."

On a cloudy, heavy day with temperatures over 30 degrees Celsius, Watson had her chances against an opponent who also went into the match having never won a match at the US Open. After dropping her serve in the ninth game, Watson saved a set point as she twice broke back when Davis served for the set. A poor tiebreak cost her the set but she recovered from 3-1 down in the second and served for it at 5-4 only to lose her way again, eventually dropping the tiebreak 7-0.

“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,” she said. “I'm fit, coming into the tournament. It's not that I'm not fit. I think it was just a mix of the tension, a bit of the stress and the heat, everything together.”

With few ranking points to defend, Watson said she hoped to climb as high as she can in the rankings, with one eye on qualification for the Olympics next summer.

The other two British players in the draw, Jo Konta and Laura Robson, are in action today, against Elena Vesnina of Russia and American wildcard Louisa Cherico.

Two top-10 seeds bit the dust yesterday with No.7 Ana Ivanovic and No.8 Karolina Pliskova going out to Dominika Cibulkova of Slovakia and American Anna Tatishvili respectively, while No.21 Jelena Jankovic also went out. But 2000 and 2001 champion Venus Williams, seeded No.23 at the age of 35, survived a tough battle with Puerto Rico’s Monica Puig, winning 6-4, 6-7, 6-3 after letting slip four match points in the second-set tiebreak.