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SYDNEY (Reuters) - Top seed Robin Soderling underlined his credentials as an Australian Open contender by overpowering defending champion Andy Roddick 6-3 7-5 to win the Brisbane International on Sunday.

The Swede's victory ensured he would move above Britain's world number four Andy Murray in the rankings and take fourth seeding for the Australian Open, which starts on January 17.

The 26-year-old stayed calm as Roddick raged through a delay while rainwater that came under the roof of the Pat Rafter arena was cleared from the court, and sealed his triumph with a 16th ace after an hour and a half.

"I'm playing really well and what makes me really happy is I never really played well in Australia before," said Soderling, who has never been past the second round at Melbourne Park.

"I didn't have the results here and now finally I have won a tournament playing really good tennis, which makes me really happy. It gives me a lot of confidence for Melbourne."

World number eight Roddick was always on the back foot in the contest and required a couple of aces just to win his first service game against the powerful Swede.

That only delayed the inevitable and Soderling, who was running the game from the back of the court, got the break at the next attempt before racing to a 4-1 lead.

Soderling summoned up another trio of aces to give himself set point four games later and went 1-0 up with a low crosscourt backhand that kicked off the line.

"He served too well today, it seemed like any time I had a look, he came up with one of those big serves," said Roddick. "I'm normally at the other side and it's better on that end of the serve."

The American continued to struggle to keep his serve at the start of the second set -- it took him seven minutes to go 3-2 up -- and the frustration boiled over when play had to be stopped.

Roddick was incensed at the way umpire Fergus Murphy had tested how slippery the court was and made it quite clear he was not prepared to take any risks before the year's first grand slam.

"I'm not going to get hurt before Melbourne," he grumbled at Murphy.

The wet weather in Queensland has left an area the size of France and Germany combined under water and Roddick after the match pledged to double his $100 per ace donation to the relief fund, boosting his contribution to $10,800.

Former number one Roddick has never been one to give up, however, and he saved all three before succumbing to Soderling's 10th break point with a netted backhand.

"We've only worked together for a couple of weeks, this is the first tournament, and it's working pretty well, no?" Soderling, who pocketed a cheque for $73,000, said of Pistolesi, who replaced Magnus Norman last month.

(Reporting by Nick Mulvenney; Editing by Alastair Himmer)