Sydney upset table-topping Perth Glory at NIB Stadium, walking out 2-1 winners in the west. Adam Le Fondre's superb poaching instincts snuck the opener, following a Milos Ninkovic header and resulting scramble in the Perth penalty area.
The result was confirmed by Danny de Silva, the perennial up-and-comer sealing the win with a cool 87th minute finish.
Perth were within inches of sneaking a remarkable comeback, Neil Kilkenny brought the match back to within a goal before Brendon Santalab's would-be equaliser in the 93rd minute was disqualified due to a controversial Joel Chianese foul on Liam Reddy.
"I'll definitely have to see the replay," Ikonomidis said. "I think we pushed well but I'm very disappointed with our first loss of the season.
"I thought we left it too late to go for that final push."
Despite Perth's precarious position at the top of the A-League tree, Ikonomidis can look forward to an Asian Cup campaign in January.
"It meant the world to me (to be selected)," he continued. "I've always wanted to be part of the Socceroos and I'll go in there with with all the confience that I've gained here."
Fellow prodigal Aussie, Danny de Silva, was not included in Graham Arnold's 23-man-squad, on the comeback trail from a lengthy injury lay off. But scoring the winner against his Socceroo rival did the Sky Blue no harm.
"It was a good match, an entertaining match, it was very good that we won," de Silva said. "There was a lot of pressure on them because they're sitting on top of the ladder.
"I was unlucky with the hamstring injuries, so it gives me a lot of confidence to score that goal. Hopefully that can fill the team with confidence.
"The Socceroos are a big aim of mine, I wish them the best in the Asian Cup and hopefully if I keep performing it will happen."