Six months later and the scepticism has turned to admiration as the Bosnia-born coach, who found time to do charity work during his earlier coaching years in Switzerland, has led an unexpected Lazio challenge for the title.
Second-placed Lazio visit Palermo on Saturday having cut Juventus' lead at the top from eight to three points in the last two rounds of matches.
Instead of smirking at his curriculum and speculating on how many weeks he would last in the hot seat, Italian critics are now singing the praises of Petkovic's motivational skills and his meticulous attention to detail.
"There is a good rapport between us and I think you can tell. I can get a decision right or wrong, but the important thing is to remain humble and united," Petkovic told reporters earlier this week.
"A house must be built on solid foundations. We have that in defence and our strikers are the first defence. Everyone sacrifices themselves for the team and in that we have found a good balance."
Petkovic, who began his football career as a midfielder with FK Sarajevo, left the Balkans in 1987 and spent the next 24 years in Switzerland, firstly as a player and then as a coach.
He coached Bellinzona, the now extinct Malcatone Agno and Lugano, all in the Italian-speaking part of the country, then got his chance with Young Boys, leading them to the runners-up spot in the Swiss Super League.
For five of those years, he spent the daytime working at the local office of the Catholic charity organisation Caritas, before taking charge of training sessions in the evening.
He ventured outside Switzerland in 2011 for a spell with Turkey's Samsunspor, but lasted only a few months.
Unbeaten in their last 14 matches in all competitions, Lazio have enjoyed the rub of the green recently with controversial wins over Cagliari and Atalanta in their last two Serie A outings.
"In some games were deserved more than we got and in other games less, but it all comes around in the end. Fortune has smiled on us but, above all, we know our strengths," said Petkovic.
Palermo are one from the bottom with only three wins and Gian Piero Gasperini has been told he must take four points from the next six if he is to avoid becoming their second coaching victim of the season.
"Gasperini has to stop complaining that the squad is inadequate and we need reinforcements," said volatile president Maurizio Zamparini. "The squad is not the problem."
Defending champions Juventus, who lead with 45 points from 20 games, have taken only one point from their last two outings and will try to stop the rot at home to Udinese on Saturday.
Their opponents appear to be recovering after a sluggish start to the season, when they were clearly affected by a traumatic elimination by Braga in the Champions League playoffs in August.
Napoli, a further two points behind Lazio in third place, visit fifth-placed Fiorentina, who are in danger of losing touch with the top three after losing their last two games.
Fiorentina have dropped five points behind Napoli and cannot afford a slip up on Sunday if they are to stay in contention for a Champions League place.