The Russian, playing her first match since losing the Australian Open final, hit only 52 per cent of first serves and committed 12 double faults in the first two sets before finding form in the decider.

"I did win. That gives me a lot of confidence. I hit a lot of double faults. I'm not always going to serve well and play my best, but at the end of the day it's about finally I was winning, that's exactly what I did today," said the top seed.

In the quarterfinals Friday, Sharapova will take on former world doubles number one Ai Sugiyama of Japan, who defeated Maria Kirilenko of Russia 3-6, 6-1, 6-3.

Earlier, defending champion Elena Dementieva breezed past fellow Russian Elena Likhovtseva 6-4, 7-5 to join Sharapova, former world number one Martina Hingis and Jelena Jankovic of Serbia into the quarterfinals.

But China's Beijing Olympics hopeful Li Na, sixth seed, fell victim to Samantha Stosur of Australia 6-2, 6-4.

"She (Likhovtseva) started to play well like she has nothing to lose and she was going for the winners down the line and she did it very good, but it's important to finish in two sets and save some energy for the next round," said Dementieva, seeded third.

"I think it's going to be very difficult to defend my title this time, but I'll try to play my best. I'm really enjoying playing here in Tokyo, it's great to be back as the defending champion," added the 25-year-old.

Jankovic needed only 62 minutes to beat China's Zheng Jie 6-4, 6-0 for her first win in three Tokyo appearances, while four-time champion Hingis downed Australian qualifier Nicole Pratt 6-1, 7-5 on Wednesday.

Fourth seed Jankovic, who has already won in Auckland this year, attributed her improved performance to giving herself a few extra days to adjust from the Australian Open courts in Melbourne.

"I've never seemed to play well here, I always had difficulties to adjust to this court, because it's a big change from Melbourne, but I did play well, especially for the first match today," said the 21-year-old.

"I had quite a tough opponent who brings a lot of ball back, but I was playing really aggressive and I tried to dictate big points, and I also served well, so it helped me a lot," said the Serbian.

In the quarterfinals, Jankovic will play her compatriot and fifth seed Ana Ivanovic, who outclassed Mara Santangelo of Italy 4-6, 6-1, 6-2.

Dementieva will take on Roberta Vinci of Italy, the winner over France's Severine Bremond 6-3, 6-0.