The 62nd-ranked Sharapova, working her way back from right shoulder surgery, avoided losing her first match in a tournament since Oct. 8, 2007, in Moscow to Victoria Azarenka. She has not lost a first round match since Aug. 11, 2003 to Elena Likhovtseva in Toronto.
Sharapova recovered from a 4-0 deficit in the first set, but then allowed a 5-2 lead in the second set to get away before dominating the third set.
"I had a pretty slow start and made a good effort to get back in the first set," Sharapova said. "I thought it was a good second set and I had a chance to close out the match, but unfortunately it didn't happen. In the third set I didn't do too many things wrong. I really stepped it up and was steady."
Sugiyama and Sharapova were scheduled to meet in Montreal last July before the former world No. 1 withdrew with her injury and sat out the next nine months.
"She stepped up and was more aggressive," Sugiyama said. "I was fighting every single point. In the third set, my knee started to hurt a little bit and I couldn't move as well as I did the first two sets. My energy went down and that's a shame."
Sharapova has won 12 of her 16 matches this year, and is 44-8 since the beginning of 2008.
"When I'm not playing tennis I don't think about it," Dementieva said after beating 54th-ranked Anne Keothavong, 6-1, 6-4. "I spent quiet time with my family."
The time off and the long flight from Russia gave Dementieva problems in the second set. She was up 5-1 and then struggled to hold off the feisty Keothavong, who's looking to reach her first career WTA Tour final after 17 ITF championships.
"For the first round it was a good match," Dementieva said. "I was playing well, but I hope to have a practice and work on some things."
Dementieva, making her debut at this event, played her first match since dropping the longest semifinal women's match ever played at Wimbledon, 6-7 (4), 7-5, 8-6. She held match point at 5-4 in the third set.
"It's not something that ticks me off," Dementieva said of the setback. "It was a good experience and a good match. I was just disappointed in the way I lost."
In other first-round matches, fifth-seeded Nadia Petrova defeated Bethanie Mattek-Sands, 6-3, 3-6, 6-3; seventh-seeded Agnieszka Radwanska beat Sorana Cirstea, 6-0, 6-1; and Monica Niculescu beat Meghann Shaughnessy, 6-1, 6-0.
"I felt very good, even with the weather -- it was very hot -- but everything worked," Radwanska said. "I'm very happy that I played such a good match and I just played two sets and I am still fresh and ready to play another match."