But hopes of an all-British final were ended when London's 15-year-old Laura Robson, the former Wimbledon girls champion, was defeated by Russia's Jana Buchina 1-6 6-3 7-5.

Watson, who defeated tournament number two seed Noppawan Lertcheewakarn earlier in the day, was delighted after a comprehensive semi-final victory over the number nine seed.

The 17-year-old from Guernsey said: "I played superb tennis today and didn't make too many unforced errors.

"I was really relaxed.

"I didn't hit yesterday and I think that was a benefit to me.

"I was hitting the ball really well.

"I wasn't getting angry at all. I was thinking about doing everything and it worked."

Watson said she was buoyed by her earlier victory over Thailand's Lertcheewakarn as the junior tournament moved indoors for the quarter and semi-final stages due to heavy rain in New York.

Watson said: "She was the one I thought would be the toughest.

"I went in with a game plan and I stuck to it."

A quarter-finalist in the Australian Open junior girls' singles earlier this year Watson, whose favourite surface is hard courts, spent time in America prior to the US Open preparing for the tournament.

Watson said: "I had been training really hard two weeks before at Bollettieri only focusing on this tournament.

"My service percentage was really high today.

"I didnt step back I just kept attacking everything.

"I was very relaxed and all in all just in a very good mood.

"I kept calm, focussed and gave nothing away."

Watson faces her doubles partner, Buchina, in tomorrow's final.

She said: "I still have one more match to go and now have to relax and mentally prepare for that.
 
"She has a killer forehand so I'm going to have to stay away from it but I'm so determined to beat her."