Perth beat the Melbourne Heart 1-0 for its first win of the season while Newcastle, yet to score a goal in three matches, drew 0-0 with Wellington.
Postecoglou ensured he left the Victory's affairs in order as he took his leave from the A-League. The win over Brisbane was their first of the season following draws with Adelaide and the Heart.
Postecoglou said the win ended a "difficult week" for both himself and the Victory as his move to the national coaching role was negotiated.
"I've carried this burden," he said. "Unfortunately, because of my circumstances this football club's had to deal with things that it shouldn't have.
"Whenever you get an opportunity like this (to coach in the A-League) you want to repay that, and I don't think I have, leaving at this point. In terms of my input I still think that the club's in great shape. But you kinda leave thinking you should have put more into it and seen it through."
Sydney again lacked direction in the absence of Italian star Del Piero, who has a calf injury. Western Sydney's own Italian import, Iacopo La Rocca, and Ono scored as the Wanderers won in front of a crowd of 40,388 the largest for a regular season match in Sydney FC's history.
"I thought the effort was there," Farina said. "We made two mistakes and again one was after a set piece it was just poor marking and we got punished for both.
"Two-nil makes it hard but they kept on trying. We just lacked a bit of creativity up front."