In the domestic political party preference poll conducted for ERR by TNS Emor - in which voters are asked who they would vote for if March 2015 elections were held today - the Center Party lost support significantly, leaving the Social Democrats in pole position.
Center Party held the top spot from June 2013 to March of this year, at which point it had the support of 27 percent of decided voters. It has now dropped to 22 percent, behind Social Democrats and Reform.
Analyst Aivar Voog attributed the change to party leader Edgar Savisaar's Crimea remarks, which were interpreted by many as criticism of the new Ukrainian government and neutrality on Russia's involvement in the crisis.
"If we look at the changes in socio-demographic terms, we see the drop took place among Estonians, among residents of areas outside Tallinn and among males," said Voog.
The Social Democrats were the most popular in April, with 28 percent support. Reform was second with 25 percent.
After a slump following being ousted from the governing coalition, IRL regained some support, rising to 19 percent. Their nationalist rival, the Conservative People's Party, had 3 percent.
The poll sampled 886 citizens of voting age.