This year’s French Open champion took three hours and 12 minutes to win her second group match, hitting 66 winners and 64 errors in an unconvincing performance.
“It was a very physical match with so many ups and downs – I wasn’t playing my best tennis, but I kept fighting,” Sharapova said.
“And when you win when you’re not at your best, it gives you extra motivation to do better in the next one.”
She added: “I’m happy to get to that stage – the goal is always to get out of your group.
“I was injured last year and didn’t play very well, so to be in the semi-finals this year makes me very proud, and especially given the way I fought tonight.”
Meanwhile, in the red group, Victoria Azarenka recovered from match points down to edge to a 6-7 (11-13) 7-6 (7-2) 6-4 win against Germany’s Angelique Kerber in Istanbul.
It means the Belarusian now needs one more victory to ensure she finishes the year as world No1, with her next opponent Olympic gold medal winner Serena Williams.
“On the two match points against me I felt I had to go for it,” Azarenka said. “I felt she would not miss, so I didn’t want to wait for her to make a mistake – I was determined to make it happen.
“I wanted to change the momentum and take destiny into my own hands. I had a clear mind of what I had to do. It takes time to go through [what’s needed] to learn that.”
In the other red group tie, US Open champion Williams beat China’s Li Na 7-6 (7-2) 6-3 to book her place in the last four.
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