CANBERRA, Jan. 12 (Xinhua) -- Top seed Serena Williams started her Australian Open title defence with a comfortable victory over Spaniard Maria Jose Martinez Sanchez 6-2, 6-2 in a warm-up event in Sydney on Tuesday.

    The American needed only 72 minutes in her first competitive match this season for a place in the quarterfinals of the Sydney International, a traditional warm-up event for the season's first Grand Slam.

    "It was a good workout," Williams said. "It was definitely getting hotter the longer I stayed out. I need to play in the heat as much as I can, so it was OK."

    Earlier, Russian Dinara Safina also reached the quarterfinals after a 7-5, 6-4 win over Agnieszka Radwanska of Poland.

    Second-seeded Safina, runner-up at Sydney before her run to last year's Australian Open final, lost the opening five games before winning nine straight to take the first set and go up a break in the second.

    She was broken while serving for the match, but broke the No. 10-ranked Radwanska to finish the match.

    "It was a little bit of slow start, but it was a start," Safina said. "It was a winning start. I was like mistiming until 5-love (down), but then I found my rhythm and my game."

    Safina was playing for the first time since a back injury forced her out of the first round of the season-ending championship in October and cost her the year-end No. 1 ranking.

    Elsewhere, third seed Svetlana Kuznetsova was upset 7-5, 6-2 by Dominika Cibulkova of Slovakia while Vera Dushevina beat Elena Vesnina 6-3, 6-4 in an all-Russian match-up.