Another rival of Olympiacos is Ethnikos Piraeus but the rivalry has lost importance when Ethnikos Piraeus was relegated from the top tier of Greek football .
Ethnikos Piraeus is the second-most successful club of Piraeus .
Another rival of Olympiacos is Ethnikos Piraeus , the second-most successful club of Piraeus , but the rivalry has lost importance when Ethnikos Piraeus was relegated from the top tier of Greek football .