Martin Torrijos, the incumbent president and leader of the Democratic Revolutionary Party (PRD), has seen his hopes of re-election damaged by inflation on basic goods in recent months and a rise in crime.
These increases have also tainted Balbina Herrera, Martinelli's closest challenger, who is a former housing minister in the governing coalition led by the PRD.
'Tired of promises'
Voters have also been put off Herrera's previous anti-US stance and her ties to past military leaders.
Economic growth in Panama is expected to fall to three per cent or less this year.
Caribbean free trade and traffic through the Panama Canal is predicted to slow, and analysts believe credit will dry up.
"We're tired of promises," Jose Cedeno, a teacher, said.
"Prices haven't stabilised."
The Panama Canal, the driver of the nation's economy, is slated for expansion during the coming presidential term.
Martinelli had a 14-point lead over Herrera in a April 23 opinion poll and will serve a five-year term if elected.
Martinelli, who runs the country's largest supermarket chain, was previously a minister of Panama Canal affairs.