World number one Maria Sharapova battled her way into the semi-finals of the Pan Pacific Open with a 4-6, 6-0, 6-1 victory over Japan's Ai Sugiyama on Friday.

The Russian, who won the Tokyo title in 2005, moved a step closer to a potential showdown with Martina Hingis in Sunday's final despite struggling mightily with her serve.

Former world number one Hingis, chasing a record fifth Pan Pacific crown, reached the last four by pulverising Australia's Samantha Stosur 6-0, 6-1.

Sharapova squandered a 3-1 lead to drop the first set but quickly recovered after a calming head-to-head with coach Michael Joyce to whitewash Sugiyama in the second.

Sharapova has dismissed on-court coaching as a gimmick but she only clicked into gear in her opening match against Italy's Francesca Schiavone following an ear-bashing from Joyce.

Watched by Japan's Prince Akishino, Sharapova made another rapid transformation after dropping the first set, winning 12 of the next 13 games to advance to the last four.

"I was giving Ai all the time in the world to do her thing," said the 19-year-old, who committed 14 double faults after an embarrassing 17 against Schiavone.

"I wasn't going for my shots in the first set. Michael told me to step in and be more aggressive."

ERRATIC SERVE

Sharapova, who faces fifth seed Ana Ivanovic in the semi-finals, admitted her erratic serve was causing her concern.

"I'm not going to win too many matches serving the way I'm serving," said Sharapova, beaten by Serena Williams in the final of the Australian Open at the weekend.

"I'm not going to get away with it against higher-ranked players."

Asked by a Japanese reporter if any tweaking of her service action was to blame for all the double faults, Sharapova snapped: "No. Don't need a translation for that!"

Hingis took just 42 minutes to book her place in the semi-finals, where she faces defending champion Elena Dementieva in a repeat of last year's final.

"If I play the way I did today I don't have to be afraid of anybody," said second seed Hingis, who won just two games against the Russian in the 2006 final. "I'll definitely want revenge."

Dementieva advanced with an easy 6-1 6-2 win over Italy's Roberta Vinci.

World number 16 Ivanovic recovered from a shaky start to defeat fourth seed Jelena Jankovic 3-6, 6-4, 6-2 in an all-Serbian quarter-final.