Melbourne, Jan 20 (IANS): Defending champion Victoria Azarenka remains on course for her third straight Australian Open tennis title after she beat American Sloane Stephens 6-3, 6-2 in the fourth round here Monday.

Stephens accidently hit Azarenka in the first set and Azarenka sent a forehand whizzing past Stephens a few games later, reports Xinhua.

Azarenka broke Stephens' serve to open the second set and then again to take a 5-2 lead. The Belarusian then had no trouble closing out the match.

Azarenka called a medical timeout after she wasted five match points when serving for the match at 5-3 in last year's semi-finals against Stephens. After leaving the court for a time-minute medical break, Azarenka returned to break Stephens' serve and to take the match but also a controversial win.

Azarenka's hopes of another victory at the Melbourne Park were boosted by third seed Maria Sharapova's surprise defeat by Slovakia's Dominika Cibulkova, 24 hours after top seed Serena Williams was knocked out.

Cubulkova knocked out third seed Sharapova in the fourth round. The 20th-seeded Cibulkova won 3-6, 6-4, 6-1 in two hours and 12 minutes.

After winning the first set, the Russian struggled with her serve from the eighth game, when she was broken at love while trying to serve out the set.

Sharapova quickly went 0-5 down in the second. She rallied to win four straight games, only for Cibulkova to serve the set out at the third time of trying.

The Slovakian then dominated the decider, setting up a quarterfinal against No.11 seed Simona Halep from Romania, who reached her career-first last eight at a Grand Slam tournament with victory over former World No.1 Jelena Jankovic.

The absence of Williams and Sharapova opens the door for two-time defending champion Victoria Azarenka and two-time runner-up Li Na.