PSG are on 69 points with four games left with Monaco trailing by 11 points
Real took the lead in the 38th minute after Rodrygo sprinted past two defenders before passing to Modric, who rifled a shot into the back of the net.
Benzema extended their lead in the second half with a penalty after the video assistant referee spotted a handball from Yeray Alvarez inside the area.
Real were reduced to 10 men three minutes from time after Eder Militao was sent off for a goalline handball.
Real goalkeeper Thibaut Courtois brilliantly stopped Raul Garcia's penalty kick with his left foot in the dying seconds.