The first is the People's Alliance of Erdogan's ruling AKP, the right-wing Nationalist Movement Party (MHP) and the nationalist Great Unity Party (BBP). The constitutional changes have allowed parties to form alliances, paving the way for Ince and Aksener's parties to join a small Islamist party in the "Nation Alliance" against Erdogan.
He mustered colossal numbers for rallies in the three largest cities of Izmir, Ankara and Istanbul on the final days of the campaign, promising a "different Turkey".
The early parliamentary and presidential elections in Turkey are scheduled to be held on Sunday, June 24, that is, nearly a year and a half earlier than planned.
Polls show Erdogan falling short of a first-round victory in the presidential race but he would be expected to win a run-off on July 8, while his AK Party could lose its parliamentary majority, possibly heralding increased tensions between president and parliament.
Inflation has zoomed well into double digits - with popular concern over sharp rises in staples like potatoes and onions - while the Turkish lira has lost some 25 percent in value against the USA dollar this year. Erdogan called the ballots more than a year early in what analysts say was a pre-emptive move ahead of a possible economic downturn.
The votes of Turkey's Kurdish minority will be especially crucial in the parliamentary poll.More news: Supreme Court sales tax ruling to make online shopping more expensive
More news: Trump renews sanctions on North Korea
More news: Xi Jinping meets Kim Jong Un in Beijing
Recep Tayyip Erdogan has won 12 electoral contests in the last 16 years.
He said the new system will bring stability and prosperity to Turkey, but critics warn it could lead to a "one-man rule".
Tens of thousands of Turkish citizens are responding to calls from the opposition to monitor the polls for a clean election from the opening of polls at 8 a.m.to their close at 5 p.m.
Mr Ince repeated an accusation made by other opposition politicians of political bias by Turkey's state media, which has given Mr Erdogan and the AK Party heavy coverage while often neglecting to broadcast opposition rallies.
But in a situation labelled as blatant unfairness by activists, the HDP's presidential candidate Selahattin Demirtas has campaigned from a prison cell after his November 2016 arrest on charges of links to outlawed Kurdish militants.
The OSCE has sent 234 observers, while the Parliamentary Assembly of the Organization for Security and Cooperation in Europe (OSCEPA) sent 72 observers, the Parliamentary Assembly of the Council of Europe (PACE) deployed 35 observers, and the Parliamentary Assembly of the Mediterranean (PAM) sent 10 observers.