Boz Scaggs Jojo help with key

[Andromeda]

I'm learning to play and sing the song Jojo by Boz Scaggs.

My issue isn't so much with the playing, it's with the key to sing it in. The original key, according to the sheet music, is in A flat minor. However, the first chord where the vocals start is a B flat minor chord.

I've transposed the song into the keys of G minor, E minor and D minor in order to see in which key I can sing it better.

I'm a bit confused. If the song is written in A flat minor and the starting note to sing is an A flat ..... but the dominant chord seems to be B flat minor....then what would be the starting notes in the keys of G minor, E minor and D minor?