The down-to-earth Ramalho is one of Brazil's top coaches, having led Sao Paulo to three consecutive Brazilian championship titles between 2006 and 2008.
Mano Menezes and Luiz Felipe Scolari are the other favourites to replace Dunga, who quit following Brazil's quarter-final defeat to Netherlands at the World Cup. Brazil are expected to announce their new coach on Friday.
"I'm just thinking about Fluminense," said Ramalho, after a second-half header from Leandro Euzebio gave his team the points in Thursday's match.
"In this type of competition, if you're not really focused on what you're doing, your players won't be either.
"When you're concentrating, it's difficult to think of something as important as the national team."
Fluminense, who won the Brazilian championship for the only time in 1984, have 22 points from 10 games, one ahead of Menezes' Corinthians.
Scolari was left waiting for his first win in his second stint as coach of Palmeiras after they blew a two-goal lead and were held 2-2 by Botafogo.
Marcos Assuncao and Kleber put Palmeiras 2-0 ahead at halftime but Jobson and Antonio Carlos replied for former South Africa coach Joel Santana's team.
Palmeiras lost 4-2 to Avai in Scolari's first game at the weekend.
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