The Italians, who must host the second leg behind closed doors due to recent racist behaviour by their supporters, are facing an uphill battle to reach the last four having lost 2-0 in Istanbul thanks to goals from Pierre Webo and Dirk Kuyt.
Lazio are yet to lose at the Stadio Olimpico in Europe this season but only two clubs have ever overturned a two-goal first-leg deficit in the knockout stages - Fulham overcoming Juventus in 2010 before Steaua Bucharest ousted Ajax at the last-32 stage this year.
Petkovic, however, is buoyed by the return of star striker Miroslav Klose to full fitness and is backing his first-choice starting XI to rise to the challenge on Thursday.
He told reporters: "We really believe we can do this. I'm really confident after what I've seen from Lazio recently.
"Lazio will go out there with the best possible 11 because we want to stay in Europe.
"If Fenerbahce are better than Lazio then they have to prove it on the pitch. We will see who's best after 180 minutes.
"But I know that Lazio have less than a 50 per cent chance of progressing following the first leg. We have to use our heads.
"The most important thing is that we will play the Lazio way, imposing our own game on them and giving them problems."
Italy midfielder Antonio Candreva echoed his coach's sentiments and rallied his team-mates to shrug off last week's disappointing trip to Turkey and progress.
He said: "We knew Lazio could do this before the first leg and we're ready to handle this game in the best possible way. We will give them a game.
"There's a lot of regret about the first leg, we should have got a better result, but this is another challenge and we know our own strength. We believe."
Fenerbahce are unbeaten in their last five European away games - without conceding on their last four trips abroad - but they have lost all of their six games in Italy by two goals or more.
The Super Lig club will be without suspended defender Bekir Irtegun and the injured duo of midfielder Belozoglu Emre and striker Moussa Sow.