The race for the leadership of the ruling Democratic Party of Japan officially started Wednesday with Prime Minister Naoto Kan going head-to-head with the party's former No. 2 Ichiro Ozawa, in a contest that will ultimately decide who will be Japan's next prime minister.

Both Kan and Ozawa, following talks held on Tuesday, filed their official candidacies on Wednesday morning for the Sept. 14 election, at the party's headquarters.

Despite reports that Tuesday's meeting between the two political heavyweights ended amicably, with the two shaking hands, many party members have commented that this kind of showdown should have been avoided in light of the economy's dire circumstances and the yen's surge.

Opinion polls indicated that Kan is ahead of Ozawa, although the former DPJ secretary general commands the direct support of 150 lawmakers and a further 60 from former Prime Minister Yukio Hatoyama's intraparty group.

Hatoyama, having first pledged to support Kan, reversed his decision in favor of Ozawa, a 68-year-old powerbroker, known for his back room dealings and embroilment in political funds scandals, but also largely credited with crafting the election campaign which saw the DPJ oust the then ruling Liberal Democratic Party ( LDP), in an historic victory last summer.

In this presidential election, rank-and-file party supporters will be eligible to vote, in addition to 412 DPJ lawmakers, as well as local assembly members.

Some analysts who previously thought Kan's victory would be a shoo-in, have since changed their position as Ozawa, despite weeks of mediation and deal-making to encourage him not to challenge Kan, has stuck to his guns and has the unequivocal support of his powerful lower house lawmakers -- joined in the belief that the current leadership needs to be changed.

Political sources close to the matter said that the 340,000 strong rank-and-file party members or supporters will sway the outcome of the vote on Sept. 14 because their votes will equal about 35 percent of the votes to be cast.

It is almost certain that the winner of the party's presidential election will become Japan's prime minister because the DPJ holds a majority in the more powerful lower house of parliament.

Should Ozawa manage to overcome his skeptics concerned over the kingpin's tainted political history and general wheeler-dealer style of politics, he will become the third prime minister since the DPJ took power last September.