Robson reaches for the stars as she eyes amazing hat-trick

Sam Stosur is next in line today for Briton who is changing the game's established order

Chris Evert, who knows a thing or two about winning Grand Slam titles, said the US Open had witnessed "a star being born". Ever since Laura Robson won junior Wimbledon four years ago the world of tennis has talked about her potential. In the space of two matches the youngest player in the world's top 100 has underlined what a glorious future she could have ahead of her.

Having beaten two Grand Slam champions in Kim Clijsters and Li Na to become the first British woman to reach the fourth round here for 21 years, 18-year-old Robson today has the chance to claim a third successive major scalp when she meets Sam Stosur, the defending champion.

The Australian will give Robson the respect she deserves. "She's probably got nothing to lose," Stosur said. "She's had two of probably the best wins of her career, and she's starting to live up to some of that potential that people have talked about from when she won junior Wimbledon when she was 14. You can't go into it lightly. You've got to be aware that she's going to come out swinging maybe and have that confidence behind her."

The achievement in beating Clijsters and Li was remarkable enough, but what was stunning about Robson's performances was the manner of the victories. The Belgian and the Chinese are both athletic big-hitters who blast opponents off the court, but Robson upset them with the power of her own shot-making and her ability to make them play the extra ball.

Robson has always had big shots – Andy Murray summed it up neatly when he said she has "very easy power and great timing" – but until this summer the worry was that her lack of speed and her sometimes leaden footwork might prevent her from reaching the top.

All that has changed in the last few months. Time and again, against both Clijsters and Li, Robson chased down shots that she would never have reached in the past and returned the ball deep and with pace. Nevertheless, she has maintained the attacking game that has been fundamental to her success. "My game is based on being aggressive, and if I don't play that way then I probably wouldn't be doing very well," Robson said.

Growing pains and injuries have held Robson back in the last two years and she believes a big factor in her recent success has been her fitness. "This summer has been the first one where I have been injury free," she said. "In the past I might have done two or three days of work. I needed a few days to get over another little niggle. This time I have just been able to keep going."

Jez Green, one of Murray's physical trainers, has played a part in Robson's transformation. "We approached Jez to see if he would have some time to work with me over the summer and he did, which has been really great," Robson said.

Even more important has been Robson's recruitment of a new coach, the Croatian Zeljko Krajan, who guided Dinara Safina to No 1 in the world rankings. "In the last few weeks I have gained a bit of confidence and the work that I have done with him has been very specific in terms of tactical stuff," Robson said. "Just in the last few matches I think it's noticeable that instead of trying to hit a winner off a tough shot like I have done in the past, I'm trying to make a percentage shot back."

Robson said she had benefited from the experience of her defeat to Maria Sharapova at the Olympics. "In that match I definitely felt like I should have won the first set," she said. "It was extremely close, and then I just made a few silly mistakes and just didn't move my feet as much as I should have. What I have been working on since then is making sure that I do move my feet, and just continuously make one extra ball and make it a little bit harder for them."

She added: "I have always thought that I can play with the top girls. Whenever I've practised with Caroline [Wozniacki] or Maria, I've always felt that the level was there. It was just taking that on to the match court and keeping the level up for the whole match."

Winning the mixed doubles silver medal at the Olympics alongside Murray helped Robson's confidence. "There were a few matches in mixed where I had to serve out in the match tie-break, so I think that helped in terms of being able to serve it out [against Li]," Robson said. "I think I'm playing better now than I was during the Olympics."

Robson and Murray beat Stosur and Lleyton Hewitt on their way to the Olympic final, though Robson said she would not be taking that match into account in her preparations for today. "I am taking one match at a time," Robson insisted, sounding like an old pro. "Sam is an amazing player and it will be a tough match."

The talk of Twitter

Judy Murray "Never mind the silver Robbo, that was pure gold baby!"

Darren Cahill (Australian coach) to Judy Murray "Laura Robson has an Aussie passport. You'd better lock her up"

Brad Gilbert "I am very impressed with LR composure for 18, can you imagine next year at Wimby?"

Heather Watson to Robson "Unbelievable Lau!!!! Keep doing ya thang girl"

Wayne Rooney "Laura Robinson is playing brilliant good luck Laura"

Robson to Rooney "Thanks for supporting! Even if you did get my name wrong"