The Russian third seed was beaten 6-3 6-4 on Wednesday by the Portuguese world number 131.
When asked why she lost to a player ranked 128 places below her, Sharapova told BBC Sport: "It was a combination of everything. I give her a lot of credit, she played extremely well today, really solid from the baseline. I don't think I was aggressive enough. I just wasn't there."
Sharapova suffered a fourth-round exit in last year's tournament at SW19.