Wimbledon champion Venus Williams also put in a solid performance, beating Virginie Razzano of France 6-2, 6-4.
Number two seed Sharapova will face 13th seed Tatiana Golovin of France on Thursday, who beat Luxembourg's Anne Kremer 6-1, 4-6, 6-2.
Playing her first match since falling to Venus Williams in the fourth round of Wimbledon, Sharapova played a steady yet lethal match, standing inside the baseline and taking big rips at the Thai's groundstrokes.
Sharapova, who has been troubled by a shoulder injury all year, also cut loose on her first serves and kept most of the points short, nailing nine aces.
"I did a lot well tonight," Sharapova, who has not won a title this year, told reporters.
"I had a few lapses but I know I can improve every match. I'm hungry and I'll put in the work, but you never know when it's going to pay off."
The Russian said she was learning to deal with her shoulder problem and was optimistic about a full recovery.
"It's still not perfect, but right now I know it's not going to get any worse," she said. "If I keep doing the right things, I know it will get better."
Third seed Anna Chakvetadze, who has won consecutive titles in Cincinnati and Stanford, took down American Meghann Shaughnessy 6-4, 6-4.
Sixth seed Daniela Hantuchova of the Slovakia beat Victoria Azarenka of Belarus 6-3, 1-6, 6-1, earning herself a third round match with Williams on Thursday.
Williams, a three-time winner in San Diego, never backed off from her powerful attack. Razzano came right at the 10th seed, but was nowhere near as accurate as her opponent.
"I made some errors, but played very aggressive and she played really well," Williams told reporters.
"She didn't give me any points and was trying with all her heart."
Eighth seed Dinara Safina of Russia, ninth seed Elena Dementieva and 11th seed Patty Schnyder of Switzerland also secured wins.
Schnyder will play fellow Swiss and seventh seed Martina Hingis on Thursday.
