Melbourne City midfielder O'Neill scored a scintillating strike 11 minutes into the December 17 derby, but it was called off 10 minutes later following a violent pitch invasion from Melbourne Victory fans.
On Wednesday night, he added another belter on its resumption - officially 46 minutes after his first, or as coach Rado Vidosic put it, three months later - to lead City to a 2-1 win and a five-point lead in the table.
In between the two, O'Neill played 14 A-League Men games, scored two more goals and earned his first two Socceroos caps.
"Coming into a game that you've already scored in is a pretty weird feeling - obviously full of confidence," O'Neill joked to reporters.
"And I think you could see that, scoring a second.
"I'm not renowned as a goal scorer either, so it was pretty crazy."
There were eerie similarities to O'Neill's first goal on Wednesday night.
In December, the midfielder enjoyed a wonderful give-and-go with Richard van der Venne before coolly finishing.
This time, he played a 1-2 with Valon Berisha and lashed home.
"It just happened really quickly," he said.
"I just saw myself in that space, I took a good first touch. Similar to the first goal, I had a good first touch and it just opened everything up for me."
The pitch invasion cast a shadow on the season and hovered over both clubs for more than three months.
"It's been been quite weird to be honest," O'Neill said.
"I don't know whether they should have given us the three points but we've done what we needed to do."
O'Neill credits his oft-forgotten first strike for kick-starting his already-excellent season.
The 24-year-old impressed on his Socceroos breakthrough against Ecuador, while he is heavily linked to a post-season reunion with former City coach Patrick Kisnorbo at Ligue 1 club Troyes.
"Football is a funny game and when your confidence is high, sometimes just when you hit the ball, it just goes in the back of the net," he said.
"It was a big weight off my shoulders just to get the first goal when that came and then I'm just brimming with confidence and just enjoying where I'm at and the future ahead of me's looking pretty good.
"Being in the Socceroos camp was a really, really special moment for me. I missed out on the the Olympics - I was involved all the way through.
"That's football as well, sometimes you don't always get that that chance or selected ... I've just used that as a bit of motivation to come back."
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