Narendra Prabhakar Gaikwad, 28, had an argument with his 60-year-old father Prabhakar Gaikwad around midnight in Dombivili town of Thane over the latter disapproving of him marrying twice, a police official said.
Following the row, Narendra attacked his father with a sharp weapon.
Hearing the noise, their neighbour Santosh Mohan Karande rushed to save the elderly man.
Narendra, in a fit of rage, attacked Karande with a knife wounding him seriously, the police official said.
While Karande died on the spot, Prabhakar was rushed to hospital, they said.
Karande's wife lodged a police complaint against Narendra following which he was arrested.
The accused has been charged under Sections 302 (murder) and 307 (attempt to murder) of the IPC, police said.