Second-placed Goias could have gone top but were beaten 4-0 away by Internacional, who closed within four points of the leaders with a match in hand.
Palmeiras have 41 points from 22 matches, Goias 38, Inter and Sao Paulo 37.
The Sao Paulo "clasico," in which Palmeiras' Ramalho came up against the club that sacked him two months ago after he steered them to the last three league titles, was a huge disappointment.
Chances were scarce and the few on target from long range were easily dealt with by goalkeepers Marcos of Palmeiras and Sao Paulo's Rogerio Ceni, rivals for the number one spot in Brazil's 2002 World Cup-winning squad.
"It's a good result. Playing against Sao Paulo here in the Morumbi is difficult," Palmeiras' former Olympique Lyon and Barcelona defender Edmilson told reporters.
"I thought it would be a nicer match, but it was stop-start, lots of marking and little technique.
"With what the teams have been showing in the championship it could have been better for the crowd."
Goias fell behind after only five minutes when 19-year-old striker Marquinho chipped over the goalkeeper.
Ten minutes later, former Inter forward Fernandao left Goias a man short when he was harshly shown a straight red card for a tackle on Magrao.
Inter immediately went two up with a shot from the edge of the box by Argentine Pablo Guinazu, playmaker Juliano headed the third six minutes after halftime and full back Kleber completed the rout with a lob 10 minutes from time.
Inter can move up to second when they host fifth-placed Atletico Mineiro on Wednesday.
Fluminense, Libertadores Cup runners-up a year ago, lost for the 12th time in 22 league matches, 2-0 at Santos, to remain rooted to the bottom of the standings, eight points below the relegation cut-off.
