From the first Anzac Day, 100 years ago next month, Australia and New Zealand have spent much more time and effort on the same side than opposing one another, confining their differences to vowels and sport.

That is what makes Sunday's cricket World Cup final between the two at the MCG unique. The tournament was a global affair with weighty geopolitical overtones, but the final will be between kissing cousins. When not playing for World Cups, they play for the rather more modest Chappell-Hadlee trophy.

That is not to say it will not be in deadly earnest. They are cousins, not twins. The two countries long have had legendary tussles at rugby and netball. New Zealand, the smaller and (in cricket terms) younger, would love to put one over the Australian cricket team, who for their part would be mortified to lose to New Zealand on such a big day and stage.

But it might at least mean the match is free of the belligerent posturing that has marked others in this tournament. New Zealand never really has played their cricket that way anyway, and under Brendon McCullum's captaincy explicitly eschews it, and so has doubly gained the admiration of the cricket world. Australia would look silly to try anything on.

Revisited daily in the prelude has been the underarm incident of 1981, on this very MCG, when then Australian captain Greg Chappell directed his brother Trevor to roll the last ball of a one-dayer along the ground to Kiwi No 11 Brian McKechnie to snuff out any remote hope of him hitting it for the six needed for a tie.

Six then meant not just over a nearby boundary rope, but carrying the faraway picket fence. In the hysterical aftermath, then New Zealand prime minister Robert Muldoon said it was fitting that Australia wore yellow. He should see the gilded livery they wear now!

In truth, the underarm moment was an exception to the rule. Australia and New Zealand don't have much aggravated cricket history. They don't have much history at all. Mostly, this reflects the balance of size and strength.

Australia are the perennial power, New Zealand an impish interloper who periodically embarrases the game's grandees and delights in it. For a while in the '60s and '70s, New Zealand played in Australia's domestic one-day competition. Until 1973, the two countries had played only one Test match, retrospectively recognised.

Former New Zealand captain Martin Crowe once characterised matches against Australia as his country's Ashes, ever covetous affairs. Australians never saw it so; they had their own Ashes. To this day, the Kiwis are beggars unable to choose; it is six years since they have appeared on the MCG in any form.

Today, though, they meet not just as big and little brother, not just as neighbours and co-hosts, but as peers. Australia are the No 1 ranked one-day team. New Zealand were ninth not so long ago, but have gathered brilliantly before and during this tournament.

The only trouble either team had in the group stages was with the other, in a riveting and antithetically low-scoring encounter in Auckland, won by the Kiwis by one wicket. It was Australia's only loss for the tournament; New Zealand remain unbeaten.

Australia are brimming with big names, reputations and egos. Captain Michael Clarke's announcement on Saturday that this final would he his last one-day international for Australia is significant only in that it acknowledges that one-day cricket has very nearly bypassed him anyway, and his exit solves a selection bottleneck. Every team should be so blessed.

Comparatively, New Zealand are obscure (their team includes chancers from Australia and South Africa) and unassuming in disposition. It makes the finalists ill-matched on paper, and might easily prove so on the ground.

Australia's collective best should be enough. But they won't presume it. Under McCullum's stout-hearted leadership, the Kiwis have grown into the proverbial team that is greater than the sum of their parts, and that equation has no upper limit. Cricket is an individual sport played in team formation, but the Kiwis very nearly have inverted that paradigm.

Their country is squarely with them. New Zealand teams once wore beige, and then grey, but now turn out in forbidding blue-and-black. It fits perfectly the favour they now enjoy in their rugby-besotted homeland; they are the Almost Blacks.

But Australia are at home, well-versed in the MCG's dimensions and accustomed to the grand occasion. New Zealand – though notional co-hosts – are strangers at and on the MCG, and never in their history have played in front of a crowd as big as expected on Sunday. It is possible they will be lost out there; others have been. It would be better for cricket if they were not.

This has been a spectacular World Cup, replete with Goliathan runmaking, but more than a few dauntless Davids, too, and deserves not just a final, but a finale.

The MCG's history indicates that whoever bats first, if they make a reasonable score, will win. But beware Australia, if New Zealand bats second and gets within six of victory, even if they are almost out of time or batsmen, for as the Kiwis already showed against Australia, and again in that wonderful semi-final against South Africa, it only takes one hit from there. And under-arm is now illegal ...