Sharapova completed a career Grand Slam by winning the French Open last year.
An incorrect call cost Sharapova in the second set. Facing a break point at 30-40, she hit a second serve that was called long to make it 4-1. The umpire climbed off his chair to check the mark and confirmed the call.
Sharapova briefly argued in vain, contending the umpire looked at the wrong mark. A TV replay showed her serve had hit the line.
She shook off the setback, sweeping the next three games for 4-all, and broke in the final game.