As you said: it's irregular :)
Another one that has only two syllables in the past tense is πήρα "I took", from παίρνω "I take".
And then there's είδα and είπα from βλέπω and λέω, respectively, and βρήκα and μπήκα from βρίσκω and μπαίνω.
And ήξερα and ήπια from ξέρω and πίνω have ή- instead of έ-.
But nearly all past tenses are accented on the third syllable from the end, with an έ- being added if the verb would otherwise have just two.