Ten-man Boca Juniors are close to joining Fluminense in the first knockout round after a 2-0 home win over fellow Argentine side Arsenal in the night's other Group Four match.
Fluminense, finalists in 2008, have taken all 12 points from their four matches, putting them five ahead of Boca with Arsenal on three and Zamora one and virtually eliminated.
Former Brazil striker Sobis came on as a substitute at La Carolina in the 75th minute and scored from a free-kick three minutes later.
Six-times South American champions Boca were the more incisive side at La Bombonera despite being a man short from the 37th minute, when holding midfielder Leandro Somoza was sent off for a second booking.
Boca went ahead in the 50th minute when striker Santiago Silva, still looking for his first goal in his eighth match, backheeled to Juan Roman Riquelme whose low shot was parried by goalkeeper Cristian Campestrini only for midfielder Pablo Ledesma to follow up and turn the ball into the net.
Silva also set up Boca's second goal one minute from time with a well-weighted pass to substitute Juan Sanchez Mino, who scored with a low shot.
"Winning with 10 men is the same as winning with 11. We're going to have to improve a lot to reach the final but we want to qualify first," Boca captain Riquelme told Fox Sports.
"Silva had a great match. He's not scoring but he's doing a great job for us," he said of the burly, shaven-headed striker nicknamed 'Tank', who joined Boca from Fiorentina in January.
With all teams having played four of their six matches in the eight groups, two more sides are virtually out of the running and Peruvian champions Juan Aurich have already been eliminated.
Juan Aurich have zero points in Group One which is led by title holders Santos on nine points with fellow Brazilians Internacional and The Strongest of Bolivia on seven apiece.
Uruguay's Penarol, one of the great teams of South America with five titles who reached a record 10th final last year, are six points behind second-placed Universidad de Chile in Group Eight. Penarol have only one point and a minus-six goals record having lost to the Chileans 2-1 on Tuesday.
Colombia's Atletico Junior are in a similar position in Group Three with one point, six adrift of joint leaders Union Espanola of Chile and Bolivar of Bolivia, and five behind Chile's Universidad Catolica.
