UPDATE 1-Tennis-Serena flexes her muscles in Sydney

(updates at end of day)

By Julian Linden

SYDNEY, Jan 13 (Reuters) - Serena Williams rebounded from her shaky start to the year with an awesome demonstration of her Australian Open intent at the Sydney International on Tuesday.

The world number two showed no signs of rustiness in her scrappy first-round win over Samantha Stosur as she demolished Italy's Sara Errani 6-1 6-2.

The American belted nine aces past her bewildered opponent in an ominous warning to her rivals ahead of next week's first grand slam of the season.

"I played a little better today but I can still improve on some things and that's what I want to do," she told a news conference. "I don't want to peak too soon, I just want to stay level for the whole season."

The powerful Russian contingent also flexed their muscles, with Dinara Safina, Elena Dementieva and Svetlana Kuznetsova all advancing to Wednesday's quarter-finals.

World number three Safina was ruthless in her 6-3 6-0 win over fellow Russian Vera Dushevina while Kuznetsova showed her determination to get out of a tight corner in her 6-2 2-6 7-6 victory over Estonia's Kaia Kanepi.

Dementieva, who won last week's Auckland Classic in New Zealand, chalked up her seventh straight win this year in defeating Slovakia's Jarmila Gajdosova 6-2 6-4.