French Open champion Sharapova finished the match with an ace but double-faults on big points almost cost the Russian the second set as the sun set over Tokyo.

"After a long match yesterday, I was just happy to win in two (sets)," said Sharapova, who had taken more than three hours to dispatch British qualifier Heather Watson the previous day.

"Obviously, I had a bit of a let-down in the second set," added the second seed, almost forced into a decider having blown a 3-0 advantage in the set before digging in to claim the tie-break 7-5.

Sharapova will next face eighth seed Samantha Stosur of Australia after last year's US Open champion beat Slovakia'sDominika Cibulkova 6-4 7-5.

"I expect a really tough match," said Olympic silver medallist Sharapova, twice a Pan Pacific Open winner, who served 14 double-faults in her opener and six against Safarova.

"Hopefully I'll play better tomorrow."