Serbian Ana Ivanovic, a 6-3 6-4 winner against France's Marion Bartoli, was upbeat after reaching the last four.
"I am definitely happy to be through. It was a tough match and I served well," she said. "We both started well but the eighth game of the second set was important. I just tried to stay low and make her run."
The meeting was a rematch of last year's quarter-final in which Bartoli triumphed on her way to the final - but here the seventh seed looked out of sorts.
Bartoli called for the doctor when she was trailing 2-1 in the second set and as she was having her blood pressure taken, she was caught on camera saying "everything is spinning".
"When I went on the court I was very dizzy and it was very hard for me to catch my breath," she said after the match.
Ivanovic's next opponent, Sharapova, faced a tougher route through, having to come from a set down to beat compatriot Maria Kirilenko 3-6 7-5 6-4.
Kirilenko, the 20th seed, had beaten Sharapova in their previous meeting at the 2010 Australian Open, took advantage of a slow start by the second seed to take the first set and a 2-0 lead in the second.
But Sharapova claimed that even at that point she was not concerned, saying: "I knew that I could have played better. If I felt like everything was going so well from my end and she was just playing so good, then I would have felt like, 'OK, well, she's just too good.'
"But I really felt like I could improve on so many things during the match and change things around. Little by little, I started doing those things better."
