Tennis: Bullish Serena issues Aussie Open challenge

The 18-time Grand Slam champion won the last of her five Australian crowns in 2010 and expressed frustration that a sixth had eluded her for so long.

With an ignominious round four exit at last year's tournament clearly still rankling, Williams said her determination to claim a "special" win was stronger than any other player in the 128-strong field.

"I've been going for number six for a number of years now -- it would be really special for me, I'd be really happy," said Williams, who is the short-priced bookmakers' favourite to win the tournament.

"I want it, I think, more than anyone else here. That doesn't mean I'm going to get it so I'll have to fight hard to get it."

The American held on to the top ranking for the entire 2014 season, ending the year with a flourish to take the US Open and the WTA Tour Championship.

Another Australian title would take her to clear second on the all-time Grand Slam winners list behind Steffi Graf's 22, having joined Chris Evert and Martina Navratilova on 18 with her win at Flushing Meadows.

Williams, 33, said it was exciting but also daunting to contemplate reaching the German great's benchmark.

"Twenty two is so far away from 18 -- when you're 18 years old you look at someone that's 21 and you think they're old," she said.

"So it's a really big distance to get to 22. I can't think that far ahead. I just have to think about 2015 at the Australian Open in particular."

Williams displayed some erratic form in the Hopman Cup this month and admitted feeling "a little off" heading into the opening Grand Slam of the season.

But she said that was not a bad thing considering she went into last year's event convinced she was in amazing form, only to crash out early to Ana Ivanovic.

"Last year I felt really good, was playing well. I was feeling amazing on the court," she said.

"This year I feel a little off. But I feel off in every Grand Slam, except for last year. That didn't work out for me, so maybe this is different.

"I still want to improve some things. I feel like I should be doing some things better, but every day I can see something coming through, so there's light at the end of the tunnel."