Panathinaikos close gap on Olympiakos
The champions had to wait until the 70th minute before Christodoulopoulos scored with a neat finish after cutting in from the right flank.
The win moved Nikos Nioplias's team on to 20 points after nine matches, one adrift of leaders Olympiakos.
Olympiakos bounced back from last week's derby defeat against Panathinaikos by thumping Panionios 5-0 on Saturday.
AEK Athens moved back into third spot with 16 points following a 3-1 home win against Ergotelis.
The Yellows fell behind to Michalis Fragoulakis's 33rd-minute strike, but skipper Pantelis Kafes, Ismael Blanco and Eder found the net to rounded off the win for Athens.