Vasco da Gama climbed to second after paying tribute to their coach Ricardo Gomes who was in hospital after suffering a stroke.
Flamengo dropped to fourth after a 3-2 defeat at lowly Avai despite two goals by Ronaldinho, one direct from a corner.
Vasco beat Ceara 3-1 and in-form Botafogo moved into third with a 3-1 home victory over Palmeiras, their fifth win in six matches.
Corinthians have 40 points from 20 matches, Vasco 38, Botafogo 37 and Flamengo 36 in the four top places that qualify teams for the Copa Libertadores, South America's club championship.
Having won only two of their previous eight matches and lost the last two, Corinthians defended top place in the standings with gritted teeth in a tough clash with relegation-threatened Gremio at the Pacaembu in Sao Paulo.
They went ahead with a penalty converted by captain Chicao (pictured) in the 18th minute and went 3-1 up after 68 minutes with goals from Paulinho and defender Ramon in the second half after Douglas had equalised before half-time with a free-kick.
The home side had Brazilian-born former Portugal striker Liedson sent off in the 69th for two yellow card offences in quick succession and 10 minutes later Edenilson was also shown the red after a booking for time wasting.
Striker Andre Lima pulled a goal back in the 73rd but southern side Gremio, in 15th place one point above the relegation zone, could not find an equaliser.
Vasco took the field at their Sao Januario stadium carrying a banner in support of Ricardo who is in intensive care in a Rio hospital after suffering a stroke on Sunday during his side's derby against Flamengo.
The 46-year-old former Brazil captain came out of an induced coma earlier on Wednesday and showed signs of improvement, according to doctors, although they could not say whether he would suffer long-term effects.
Vasco had a comfortable win as they chase a double, having already won the Copa Brasil, which guarantees them a place in the Copa Libertadores, earlier in the year.
Copa Libertadores holders Santos scored three goals in the final 15 minutes, two through striker Borges, as they came from three goals down for a 3-3 draw away to Internacional in Porto Alegre.
