Edgardo Bauza's side dropped all three points at home to Gimnasia La Plata on Saturday but responded in style against lowly Olimpo.
Mauro Matos opened the scoring in the 42nd minute for the hosts, rounding goalkeeper Nereo Champagne before shooting from an angle.
And despite the best efforts of Nestor Moiraghi, San Lorenzo took the lead as the defender could not keep the ball from going into the back of the net.
Ivan Alejandro Furios then hauled down Gonzalo Prosperi in the penalty area five minutes into the second half.
And Nestor Ortigoza's penalty was first-class, as he give Champagne no chance with an expertly struck spot-kick that flew into the bottom-left corner.
Two goals were more than enough for San Lorenzo, who climbed to ninth with their victory.
Olimpo sit in 17th place with just two wins from nine matches.