Four World Cup titles under the belt but defending champions Australia are not exactly the favourites this time as they start their campaign for a fifth trophy with a tricky opener against Zimbabwe at the Sardar Patel Motera Stadium in Ahmedabad on Monday.

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Australia have been unbeaten in 22 matches in the last two tournaments played in South Africa (2003) and West Indies (2007), under Ricky Ponting.

They have won 23 back to back matches stretching to 1999 and have been unconquered in 29 ties, which includes the unforgettable tied match against South Africa in the semi-final 12 years ago.

On paper, Ponting's men hold a clear edge over the African nation led by Elton Chigumbara, but would be eager not to be tripped by the one-time minnows of the 50-over game as was the case 28 years ago in England.

The Aussies, fresh from a 6-1 rout of their Ashes nemesis

England in the following ODI series at home, landed in India only to be rudely awakened by successive defeats in their two practice games against India and South Africa at Bangalore.

But they are sure to hit the strap on the run when their bid to clinch their fifth World Cup crown starts.

The Aussies have a fine batting line-up in which Shane Watson, who opens the batting, and Ponting are crucial in the top order to lay the platform for others to build upon.

But a question mark remains over the ability of the middle order batsmen in playing spin bowling on Indian pitches.

Watson has performed brilliantly with the bat in ODIs in the last year, having scored 832 runs and Zimbabwe's think tank would have talked about ways of stopping the Queenslander from taking the game away.

"It's much different and bigger responsibility in opening the innings than batting at number seven in the last World Cup, a role Adam Gilchrist and Matthew Hayden did so beautifully throughout their career. It's a great responsibility and I'm looking forward to that challenge," said the 29-year-old.

Ponting, whose fabulous innings of 140 not out in 121 balls in the 2003 World Cup final buried Indian hopes, has come back into action after a long injury lay-off following a broken little finger sustained during the Ashes series against England, but he has quickly got into his stride with good half-century knocks in two practice games.

It's the form of the others, which is a big worry for Australia. Without the presence of the injured Michael Hussey, who was adept in playing the slow bowlers on previous visits to the sub-continent, they lack a batsman around whom the other quick run-getters like Cameron White can play around.

The Indian spinners exposed the chink in the Aussie batting armoury in the practice game when they triggered a collapse and helped the hosts defend a meagre total with aplomb.

Though not too much needs to be read into the practice ties, as Watson insisted yesterday, Zimbabwe's think tank would surely have noted this stuttering performance with some glee as their own attack revolves around spin rather than pace as was the case in the past.

In bowling, Australia have a pace attack that can be handy for opposing batsmen even on the slow and low sub-continental wickets.

The biggest plus for them has been the return to what looks like the form of his old by spearhead Brett Lee who is expected to open the bowling with sling-arm action and speedy Shaun Tait with left-arm Mitchell Johnson coming in as first change.

Australia have an excess of riches in pace and medium pace with Watson and John Hastings, who is expected to play, coming in behind the top three.

But they lack a top class front-line spin bowler barring Jason Krejza, who has been recalled after several months, to bowl the middle overs when the field is spread out.

Zimbabwe have not been hot property in ODIs over the last few months and barring a few victories over a less than full-strength India at home, have not really been up to the mark.

They have a reasonably sufficient batting line-up in which Brendon Taylor stands out with his ability and experience, but can find the going tough against the Aussie pace attack.

Zimbabwe are hoping that a spin-oriented attack, consisting of former skipper Prosper Utseya, left-armer Ray Price and Graeme Cremer would do the magic against the middle order of Australia.

"It is going to be tough to play the first match of the World Cup before the defending champions Australia. But I think the guys are prepared," leg spinner Cremer said.

Cremer also said the bowlers were learning the tricks of bowling on sub-continental tracks by watching seasoned bowlers like India's main trump card Harbhajan Singh.

"We have watched Harbhajan (Singh) bowl. At what speed he bowls and what length he bowls. It is good for us. And on the last tour to Bangladesh (in December 2010), we saw how our spinners bowled and their spinners, and there tracks are pretty similar to here," said the 24-year-old with 47 One-day wickets to his credit.

"Spin is one of our strengths with which we could take on the Australians, which is a tough team. We ought to restrict them to a low score," said Utseya.

Even with these factors which are likely to help them, the Zimbabweans have a huge task on hand in taming the three-time defending champions and cause the first big upset of the tournament as was the case in 1983 in England.