Chinese player Li Na has advanced to the last four at the Sydney International after beating American qualifier Madison Keys on Wednesday night.
Li took over two hours to get past the US teenager as she had to come from a set down.
The fourth seed eventually beat the sixteen-year-old 4-6, 7-6 (2), 6-2.
Li's win has set up a semi-final showdown with top seed Agnieszka Radwanska on Thursday.
Li Na won the event in 2011 and was runner-up to Victoria Azarenka last year.
Earlier Agnieszka Radwanska beat Italian Roberta Vinci in straight sets 6-4, 7-5.
Second seed Angelique Kerber of Germany was a straight sets winner over Russia's Svetlana Kuznetsova.
Kerber will meet unseeded Dominika Cibulkova in the semi-finals.
Students take exams without invigilator in Hangzhou