Melbourne, Jan 17 (IANS): Reigning US Open champion Samantha Stosur became the first big casualty in the Australian Open tennis tournament here after losing 6-7, 3-6 to Romanian Sorana Cirstea in the women's singles first round Tuesday.

Defending champion Novak Djokovic stayed cool under Melbourne's hot weather to thrash Italian Paolo Lorenzi 6-2, 6-0, 6-0 in a men's singles first round tie.

World No.60 Cirstea shocked the Rod Laver Arena crowd as she disposed of her Australian opponent in just 91 minutes. The Romanian played some brilliant ground strokes as she notched 28 winners to Stosur's 12.

Djokovic started his title defence shakily, losing the third game of the first set. However, the World No.1, playing his first match of the year, showed his class as he won the last 16 games in a row to complete the rout.

The two-time Champion here next plays Colombian Santiago Giraldo, who beat qualifier Matteo Viola of Italy 6-4, 6-2, 6-1.

"Obviously I want to get a good start of the year in my first official match of the season, I have decided not to play the opening week of the year in order to get ready for Melbourne. I am satisfied with the overall performance today," said Djokovic.

The Serbian also won the Wimbledon and US Open last year. His only loss at a major in 2011 was in the semifinals of the French Open.

In another women's first round match, fourth-seed Maria Sharapova sailed through to the second round with a ruthless 6-0, 6-1 victory over Gisela Dulko of Argentina.

The 2008 Australian Open champion took 58 minutes to close the match. The Russian, who hit 14 winners to the Argentine's four, was brilliant at the net, not giving the 68th-ranked Dulko any chance to settle down.

Dulko had beaten Sharapova at the 2009 Wimbeldon.

Sharapova will play American Jamie Hampton in the second round.

Following are the results so far of Day Two at the Australian Open:

Women's singles first round:
Sorana Cirstea, Romania, bt 6-Samantha Stosur, Australia, 7-6(7-2), 6-3
4-Maria Sharapova, Russia, beat Gisela Dulko, Argentina, 6-0, 6-1
2-Petra Kvitova Czech Republic, bt Vera Dushevina, Russia, 6-2, 6-0
18-Svetlana Kuznetsova, Russia bt Chanelle Scheepers, South Africa, 6-3, 3-6, 6-0
14-Sabine Lisicki, Germany, bt Stefanie Voegele, Switzerland, 6-2, 4-6, 6-4

Men's singles first round:

1-Novak Djokovic, Serbia, bt Paolo Lorenzi, Italy, 6-2, 6-0, 6-0
17-Richard Gasquet, France, bt Andreas Seppi, Italy, 6-3, 3-6. 6-3, 6-1
24-Kei Nishikori, Japan, bt Stephane Robert, France, 6-1, 7-6, 6-0
4-Andy Murray, GBR, bt Ryan Harrison, United States, 4-6, 6-3, 6-4, 6-2
5-David Ferrer, Spain, bt Rui Machado, Portugal, 6-1, 6-4, 6-2
14-Gael Monfils, France, bt Marinko Matosevic Australia, 7-6(7-5), 6-3, 6-3