It is more likely that long-serving leader Erjavec will remain at the helm of DeSUS, political analyst Andraž Zorko, who works for the pollster Valicon, has told the STA ahead of the congress.
Erjavec has been leading the party for 15 years and is considered by many to be unbeatable. The incumbent is counting on getting delegates on his side by stressing his achievements, while Pivec's trump card is her call for leadership reform.
Local councillor Borut Stražišar is vying for the post as well, but he has mostly remained out of the spotlight during the campaign.
The duel, a rare competitive confrontation in Slovenian politics where rubber-stamping of unopposed candidacies is the norm, has already affected the power dynamics within the coalition.
Prime Minister Marjan Šarec, who explicitly said he did not want to get involved in the presidency campaign, tentatively endorsed Pivec despite allegations of misdeeds in her earlier job, while openly criticising Erjavec and his handling of Slovenia's troop withdrawal from Iraq.
This has led Erjavec to accuse the prime minister of pulling strings all along, trying to break up DeSUS and using Pivec for that. Erjavec told Delo newspaper that Šarec had attempted the same with Labour Minister Ksenija Klampfer, whom he would have preferred at the helm of the Modern Centre Party (SMC) over Economy Minister Zdravko Počivalšek.
DeSUS has long been a kingmaker in Slovenian politics, providing majorities for almost all right-leaning and left-leaning governments since 1997 – the reason why Erjavec has been such an irreplaceable figure at the top, according to Zorko.
In the recent period, though, the circumstances have changed: DeSUS did poorly at the last general election, losing half of its MPs, as well as recording a dismal result at last year's EU election.
These two events created an opportunity for an honourable resignation. Erjavec did indeed propose stepping down, but the party rejected his offer, giving him a vote of confidence and thereby simply confirming there is no alternative, says Zorko.
In the light of this, Pivec's bid came as a surprise. And while it has rocked the boat, it will probably not be enough to overthrow Erjavec, Zorko believes.
Regardless of the outcome of the race, the future developments are moot.
If Pivec wins, what follows is quite uncertain, notes Zorko. Erjavec's victory would also open up a number of possibilities, ranging from a continuation of the status quo to some DeSUS members leaving the party or even DeSUS becoming part of a new coalition that the opposition New Slovenia (NSi) appears to want to put together.
And although it seems Erjavec is on track to win, this is by no means a given.
"Even though it seems that Erjavec has secured support within the party, that he has many more opponents outside the party than within it, that all attacks against him by Šarec consolidate his support rather than undermine it, this election … is still definitely riskier than an unrivalled contest," says Zorko.
Heading into the congress, three out of five DeSUS MPs have backed Erjavec, including DeSUS deputy group leader Franc Jurša, who has accused Pivec of being dedicated neither to the party nor to its deputy group. Pivec, on the other hand, enjoys the support of certain influential DeSUS officials, including former Health Minister Tomaž Gantar.
Erjavec has issued an appeal ahead of the congress urging DeSUS members to support him and thus prevent the party from falling into the hands of other parties, seen as the strongest implication yet that he thinks Šarec is trying to get rid of him.
Pivec has responded to his statements, saying she was not holding the party hostage and had not received any special treatment from Šarec.