NEW YORK, USA (AFP) — World No 1 Victoria Azarenka advanced to the US Open semi-finals for the first time yesterday while Russian third seed Maria Sharapova struggled before rain left her match postponed until today.

Reigning Australian Open champion Azarenka defeated seventh-seeded defending champion Samantha Stosur, 6-1, 4-6, 7-6 (7/5), ensuring the 23-year-old top seed from Belarus will remain atop the world rankings no matter how the Open goes.

Sharapova was forced to stop, first by rain and then by US Open officials, who ordered the completion of her match pushed to Wednesday when showers struck for the third time on Tuesday with French 11th seed Marion Bartoli leading 4-0.

That left Azarenka to wonder who would be her foe in her first US Open semi-final on the Flushing Meadows hardcourts in the year's final Grand Slam tournament. Azarenka leads Sharapova 5-4 and Bartoli 8-3 in career results.

Today's other quarter-finals will send US fourth seed Serena Williams, a 14-time Grand Slam champion, against Serbian 12th seed Ana Ivanovic and Italian 10th seed Sara Errani against 20th-seeded compatriot Roberta Vinci.