Djukanovic's Democratic Party of Socialists (DPS) declared him the victor on the evening of April 15.
The Center for Election Monitoring (CeMI) projected Djukanovic winning over 53 percent of the vote, which would give him an outright victory in Sunday's election.
Mr Djukanovic has been accused by the opposition of being linked to the mafia, which he denies. None of the remaining six candidates reached double digits.
Voting has begun in Montenegro with pro-western former prime minister Milo Djukanovic expected to be elected president of the small Balkan country.
"After this overwhelming and superior result you should reconsider your political position", he said in a direct message to opposition leaders.
Sunday's vote passed off peacefully amid fears of disorder after 20 people were arrested and accused of trying to stage a coup during legislative elections in 2016.
"For so many years we are awaiting changes in Montenegro and I am assuming that will happen today in a democratic way that Montenegro deserves", Radmila Cagorovic, 66, a retired schoolteacher said after casting her ballot in Podgorica.
His main opponent is Mladen Bojanić, a businessman supported by several parties, including pro-Russian contingents.
The country has also been marred by organized crime, with about 20 people killed by assassinations or vehicle bombs over the last two years. "I am confident that in the next five years we will make the final steps and achieve results that we have been planning to achieve on our 20-years-long road to European Union membership", he added. Bojanic is expected to secure a third of the vote.
His presidential candidacy is supported by the ruling coalition partner Social Democrats, as well as Bosniak, Croat and Albanian minorities. The pro-Russian candidate, Marko Milacic, came fourth with 2.7 per cent of the votes.
For Djukanovic, however, the choice between Brussels and Moscow is crucial to Montenegro's development.
In 2016, he defied Russian Federation by spearheading Montenegro's accession to North Atlantic Treaty Organisation.
But he has toned down the anti-Russian rhetoric, saying he wanted "normal relations with Russia if it is prepared to do the same".
The EU in its 2016 country progress report told Montenegro it should continue its efforts to reduce organised crime, in particular on human trafficking and money laundering, and also noted the problem of worldwide cigarette smuggling through the port of Bar.
The last turnout figures, one hour before the closing of the polls, was 58.5 percent, down from the 2016 elections.