Pahor, who has been at the helm of the party for 15 years, was defeated amidst calls for a leadership change and the party's clearer positioning on the left as well as criticism that he was too pro-government.

Lukšič, education minister in the Pahor government in 2008-2011, won 190 votes in the second round of balloting against Pahor, who mustered 180.

Patrick Vlačič, who served as transport minister in the Pahor government, and fringe candidate Zlatko Jenko were eliminated in the first round, in which Pahor secured a plurality of votes.

After election, Lukšič announced a tougher attitude to the government, especially its bad measures. "What this government is doing isn't good for Slovenia...it's not right it is dismantling systems that are good."

He said that the congress had "mustered a will for change, to go left," but added that "the will is not as strong as some of us had expected", so much effort would be needed to move the party further to the left.

Congratulating his successor, Pahor expressed his full readiness to cooperate, while noting that Lukšič had a major responsibility running the party in what he said were challenging times.

Pahor is bidding his farewell with a satisfaction. Despite the change, the SD will remain a pillar of stability in the Slovenian political arena, also because the "change will not cause an internal rift", he said.

Some of the around 380 delegates at the congress highlighted Pahor's achievements, but even more criticised him for alienating himself from the party and for being too supportive of the centre-right government.

Such a view was also offered by Lukšič in his address earlier today when called for a strong left, which he said was "the best thing for Slovenia".

"A party that does not have the ambition of becoming a leading party is not my party," Lukšič said in his address, adding that the SD needed a president that would speak with a sense for what the left felt.

Presenting his bid, Pahor admitted the party had problems with its identity as well as with the challenges of the time. "But we survived politically when many fell, and we have exceptional potential for new feats."

He said that the main challenge for the country and the party was how to restart economic development while distributing the burden of a lowering in the standard of living fairly among the citizens.

Vlačič meanwhile warned against the politicians spreading fear among people, saying that in fear people were prepared to accept a reduction in democratic standards.

He moreover called for equality so that everyone can develop their potential, and maintained that the wealthier should contribute more to society.

The vote may have been tipped in Lukšič's favour by Pahor's announcement of his intention to stand in the autumn presidential election, where he is to compete with incumbent President Danilo Türk for the support of the centre-left electorate.

Pahor expressed his belief that the presidential bid was compatible with his candidacy for the top job at the SD, and that his standing was good for the party.

Yet some of the delegates were surprised by the announcement, reproaching Pahor for his failure to seek the party's consent to his presidential bid. Unofficially, the view went that he had cornered and used the party.

Others maintained that the congress was supposed to answer the question of the future role for the party, rather than what Pahor would do in the future.

The delegates endorsed the proposal to meet for another congress in a year to determine the party's future platform and calls were heard for the party to stick to the values of social democracy.

The congress also elected four vice-presidents, two of each gender. MEPs Tanja Fajon and Mojca Kleva, as well as MPs Bojan Kontič and Dejan Židan were elected in the first round.

Uroš Jauševec was re-elected secretary general, while Dejan Levanič was elected president of the SD conference.