Palmeiras joined Atletico Mineiro, shock 1-0 losers at home to Goias, at the top of the Brazilian championship standings with 28 points from 14 matches.
Atletico lead by a difference of one goal.
The two teams are four points ahead of Vitoria, who beat Coritiba 1-0 at home, and Internacional, who went down 3-2 away to Botafogo on Saturday.
Palmeiras, unable to fly due to poor visibility on Saturday, had to make a 570-km bus trip to the city of Presidente Prudente where the derby was played to avoid crowd trouble in Sao Paulo but still turned in the better performance.
Ronaldo, who fell badly on his left arm, had to leave the field after 20 minutes and Corinthians doctor Paulo de Faria said he had "a suspected fracture of the hand, he hurts a lot and cannot play."
The three-times FIFA Player of the Year will undergo tests on the injury on Monday.
NINE-HOUR JOURNEY
Unlike Corinthians, who managed to fly on Saturday to the match venue, Palmeiras only arrived at dawn on Sunday after a journey of almost nine hours.
"Everyone was quite tired, but overcoming that was the challenge and the team did more than that," said 26-year-old former Flamengo reserve Obina, who joined Palmeiras in May.
"The afternoon belonged to a battling team...that did the utmost to get the result," the striker told reporters.
Obina opened the scoring in the 32nd minute when he headed home a cross from the right by midfielder Pierre and converted a twice-taken penalty on the hour after a push by Corinthians captain Chicao on Cleiton Xavier.
The striker, who had two other goals ruled out in marginal offside decisions, completed his hat-trick with his eighth goal for the club five minutes later, tapping in a pass from Xavier.
Corinthians had substitute Alessandro sent off 16 minutes from time.
Former Inter Milan striker Adriano helped Flamengo end a run of three consecutive defeats in a 2-1 win at Santos, with his 78th minute shot from outside the box drawing his side level.
Substitute Robson had put Santos in front and an own goal by defender Para three minutes from the end gave Flamengo the points in their first match since they sacked coach Cuca.
