O'Neill, the Perth-born son of an Irishman who boxed as an amateur and then won all four of his professional fights back in Leinster, showed the family's fighting spirit as he described the attitude it was going to take for his team to beat the A-League champions at Allianz Stadium on Saturday night.

"Every time you play against them you know you're in for a tough game, but if we show up on Saturday like we have done and defend very well and attack very well there's no reason why we can't win this game," O'Neill said.

"They're a proven good team, but we're very optimistic and very keen to prove ourselves. We know we're better than Melbourne Victory. Slowly but surely we'll come to the fore and starting this week we'll kick on and show the competition what we're about.

"You have to believe you can beat the opposition, because if you go into a game thinking 'oh, we might be off, we might get rolled here' then there will only be one outcome, that you're going to lose.

The last time these two teams met was in the grand final in May, when Victory won 3-0 at AAMI Park.

If any of the Sydney players have psychological scars left over from that match then O'Neill can't be one of them because he only joined the club from Perth Glory at the end of last season, but he is adamant everyone at Sydney is going in with the same belief he has.

"It's not something we have to talk about," O'Neill said. "Individually and collectively, as a team, we know we've got some very good players who are also very good team players and I think the confidence that comes from that flows into match day.

O'Neill said Victory win a lot of games before they even kick off because opponents are hesitant to take them on and just try to hold them in the hope of getting lucky.

"I think their main thing is that they try to intimidate in a lot of games they play and if you go in and let that take hold and let them take control you're in for a very tough game against them, because they're good at that," he said.

"They won the league, the championship and the FFA Cup and that definitely speaks a lot for them, but I think it's time for a team to stand up against them and give them a good shake and I think this Sydney FC team can definitely do that."

O'Neill said the second half of the FFA Cup final last Saturday offered genuine hope to teams playing against Victory. Perth, two goals down at halftime, changed to a more attacking formation and pushed hard from there.

"Victory had a very good first half, but you saw in the second half Perth started to come back into it and to be fair they were the much better team in the second half and they created a lot of chances," O'Neill said.

"That's very positive for A-League teams because if Victory can get dominated in the second half like they did in the FFA Cup game there's no reason Sydney FC can't come out from the first whistle to the last whistle and dominate the whole game. That's the mentality you have to go in with.

"You don't have to go crazy out there, you've just got to be positive and put on a very professional performance. We'll aim to do that in front of a very good Sydney FC crowd and hopefully we'll all go home happy."