The power-hitting 19-year-old had to battle through a re-occurrence of the thigh injury that forced her to withdraw from Wimbledon last year to set up a semi-final against top seed Serena Williams on Friday.

"I felt it since the beginning. It's been tight, but it's been something that with some treatment its been fine," Keys told reporters after she needed an injury time out during the second set of her match with Venus.

"Then one shot in the match, all of a sudden I felt it kind of really get tight. I thought I was close to pulling it.

"I ignored it at Wimbledon and tore it, which ultimately made me have to withdraw. "At that moment, it was kind of a panic of 'I need to get some tape on this so I don't do that again'."

"It's one of those things where it's probably going to hurt, I'm probably going to have tape on it, but I'm just going to do my absolute best and enjoy the moment."

Her movement was curtailed after she got her thigh strapped but the world number 35 continued to produce the clean ball striking that has characterised her tournament as she slammed 34 winners.

"I knew I couldn't run as much," said Keys, who enjoys eating Australian Tim Tam chocolate biscuits after each victory. "I knew if I was going to get stretched out it was going to be more painful.

"It was kind of that thing if you have it, go for it, because I'm probably not going to last that long in a rally. "That's kind of what I did."

Keys, who took up the sport after watching the Williams sisters as a child, said she had been nervous at the start against Venus but would try to dampen those feelings when she plays Serena.

"It's just one of those things where I have to go out and I have to do my best and I have to really just have to stay focused," she said.

"She's obviously very, very good and she's going to play very well. I get too focused on what she's doing I think I can kind of let the moment get away from me.

"So I'm just really going to stay focused on myself."

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