Her 6-4 6-2 victory means she will climb to third in the rankings and can finish the season on a high in Sunday's final against either Serena Williams who came through against Jelena Jankovic.
Li, who took only three games when she lost to Williams at Flushing Meadows in September, said: "At the U.S. Open (semi-final) I had already lost the match before I came to the court.
"Maybe now I have to try to focus on what I should do on the court, not focus on what she does, so I have to try to play my game and not follow her," the 31-year-old said.
Her coach Carlos Rodriguez said Li needed to show more self-confidence to go out and enjoy her matches but she explained it was a problem dating back to her beginnings as a player.
"I always try, but sometimes it doesn't work, you know. And also, I think when I was growing up, I did not learn to feel that confidence, I cannot show how good I am, because when I was starting to play tennis, when I won a tournament, the coach was so tough," she said.
"If I won a tournament and the next day I was training, if I made a mistake, for sure she would say, 'What? You just won one tournament. Are you thinking you can win another one? Why don't you train harder?'
“I think she always punched me at the time, so that's why. I didn't have the confidence to show how good I am."
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