The former Blackburn Rovers striker slotted home at the second attempt in the 68th minute after seeing his initial header saved by Alexandros Tzorvas from Lomana Lua Lua's cross.
Panathinaikos created a host of chances in an absorbing match at the Olympic Stadium, with Greece striker Dimitris Salpingidis and France marksman Djibril Cisse both hitting the crossbar.
Olympiakos have cut Panathinaikos's lead at the summit to four points. The Greens are on 61 points while last season's champions have 57 with three matches to play.
PAOK Salonica, who occupied second place before Sunday's games, were knocked down to third spot by Olympiakos after they slumped to a 1-0 home defeat to AEK Athens.
Ismael Blanco scored the only goal after 19 minutes.
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