Osieck, sacked by Australia 16 months ago after successive 6-0 defeats against France and Brazil, was watching on at Kaiserlautern's Fritz-Walter-Stadion as Troisi, and his green and gold team-mates, produced the style and guile he could never inspire them to during his reign.
And Troisi fired back at the man who in the German press derided him as no more than a bench player, declaring: "I saw what he said and that's his opinion, football is all about opinions.
"I know that he didn't like me for whatever reason and I didn't play for nearly two years (while he was in charge) for the Socceroos.
"I have no idea why but I'm back and doing what I should be doing on the park.
"I don't play for him and his opinion doesn't matter at this point in time. What matters is the gaffer's decisions and obviously he's happy with me, and I am playing well."
Osieck told the German Football Association website: "He (Troisi) scored the winning goal in extra-time against South Korea in the final of the Asia Cup, although Tomi Juric deserves most of the credit for the goal following his solo-run.
“For me personally, Troisi is not starting XI material. I would go with Tommy Oar.”
Troisi, who grabbed Australia's equaliser in the 40th minute with a powerful header from Nathan Burns's cross, made seven appearances during Osieck's time in charge before falling out of favour with the German.
He put Australia's performance into perspective when he added: "If you told me 12 months ago that we would come to Germany and nearly beat the world champions I wouldn't have believed it.
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"It's amazing how far the team has come and the style of football we are playing, we put Germany under the pump and when we look back at over the next couple of days we will be disappointed not to have won.
"We had a lot of chances and if we had put a couple of them away it would have been different. But we let them back in it a little bit.
"But that's what friendlies are like ... it's just good to see we are moving in the right direction."
Asked if he thought a Germany side sprinkled with the old and some of the new had been surprised by Australia's intensity and technical adaptability, he replied: "I don't think they expected us to play the way we did and put them under so much pressure.
"You could see out there they weren't comfortable at all ... it was fantastic to see.
"It was tough out there at times - they are the world champions after all but we took the game to them.
"No matter who we are up against the boss wants us to play football and it's my job to create and score goals and that's what I am doing at the moment."
Troisi posted to his Instagram followers after the match with another message to any doubters. "We have come a long way in so little time. Still a lot of work to be done but great to see Australian football moving in the right direction and we will continue to work hard, learn and keep improving as a team," he wrote.
Involved in most of Australia's many creative moments, Troisi played with perception and poise and was always available to play a team-mate into space, evade a tackle and drive the Socceroos forward in what was one of his most telling displays for his country to date.
With his future not decided beyond this season when his loan from Juventus to Zulte-Waregem expires, his impact on the match would have impressed many watching scouts.
"I've had a good season in Belgium and the Asian Cup was fantastic," he added. "Obviously putting on performances against quality opposition like this also helps.
"I still have a year left of my contract with Juventus and will play out the season and talk with them at the end of the year and go from there."
