By Ed Osmond
"I felt like I started off really slow and she started off really well," Sharapova told reporters. "Quite the opposite of me, I think she was much more aggressive than I was in the beginning.
"I think I was playing too much defense and she was serving really well."
Fifth seed Sharapova grew increasingly tetchy as the crowd sensed a huge upset, making a few unsuccessful challenges to line calls and talking to the umpire.
Left-hander Robson served well and struck several fierce forehand winners against the three-times grand slam winner and former world number one who won the Italian Open this year to underline a return to form.
The crowd slow hand-clapped as they waited for the line calls to be reviewed but Sharapova managed to claw her way back into the set and forced a tiebreak.
Former junior champion Robson, the world number 254, continued to cause problems and the set hinged on the point played with Sharapova leading 5-4.
Robson had a shot called out which she challenged and the replay showed the ball landing just one centimeter outside the line to huge groans from the crowd.
Robson continued to produce the odd stunning forehand winner but Sharapova struck a barrage of piercing groundstrokes and served more consistently to surge into a 5-1 lead in the second set.
Robson refused to lie down, however, and she won two games in a row before Sharapova clinched victory in one hour 48 minutes.
"I don't think she had anything to lose in this match," said Sharapova who next plays Czech Klara Zakopalova.
"I think that brings out the best in someone when they go out and they play free and they just go for the lines."
(Editing by Ed Osmond)