The No. 3 seed got out to an early lead after she broke her countrywoman twice, got 81 percent of her first serves in and looked absolutely dominant.
After that 31-minute first set, it appeared the 30-year-old Petrova was going home in a hurry.
Not so fast.
The powerful Petrova responded by breaking Sharapova thrice (with a little bit of help from Sharapova's 20 unforced errors) in the second set en route to a 6-4 set win. After she broke Sharapova yet again and took a 2-0 lead in the deciding set, this one looked over yet again, just in the other direction.
Then the rain came.
After a long break, both women came out with a new-found energy, but Sharapova had decidedly more.
How far will Sharapova advance?
Petrova had a chance to jump to a 3-0 lead in the final set after a couple of aces put her up 40-15, but four straight points from Sharapova won her the break, and for the third time, completely turned around the match.
The younger Russian went on to break Petrova one more time and advanced to the quarters where she will face Marion Bartoli.
The 25-year-old Sharapova won the French Open earlier this year, but this might just be her greatest accomplishment of the season. After winning in New York back in 2006, she failed to make it to the quarterfinals five straight years.
That ugly streak is finally over, and if we couldn't say it before, I think it's safe to say Maria Sharapova is finally back.
If she manages to get past Bartoli, who she is 3-0 against in her career, World No. 1 Victoria Azarenka likely awaits in the semis.