Fabian Schar's early header proved enough to see off Albania 1-0 in an emotionally charged encounter at the Stade Bollaert-Deleis that drew much attention for the peculiarity of Switzerland midfielder Granit Xhaka facing off against his brother Taulant.
But Petkovic's men struggled to put away opponents operating with 10 men following Loic Cana's first-half red card and, in light of Romania's creditable showing in defeat versus hosts France in the tournament opener, the former Lazio boss wants to see them work through the gears in Paris.
"I always try and look at a team overall and I was impressed by the Romanian side as a whole," Petkovic said of their last-gasp heartbreak at the hands of an inspired Dimitri Payet.
"They did a great job and caused France a lot of problems - France are an excellent side
"From a physical and psychological perspective they were doing very well. We will see if they can match that coming into this game.
"What we gave against Albania probably won't be enough against Romania."
An enviable collection of creative talent in Petkovic's ranks is a key factor in Switzerland being viewed as favourites for the capital clash but the 52-year-old suggested the onus should be on Anghel Iordanescu's men due to their status as group winners during qualification.
"I've never said that anyone is a favourite but I think when someone finishes first then I give them a bit of an advantage," he explained.
"For this match, what will matter most is who approaches the game better. We really have to up the tempo throughout the 90 minutes because we've really seen that this Romanian side are able to play at a certain tempo for 90 minutes and they can threaten the opposition."
Despite already having three points on the board, Petkovic bridled at the prospect of playing for a draw.
"With three points and qualification, clearly we want to do things correctly to write a great chapter in Swiss football history," he added.
"Switzerland have never succeeded in winning two group matches so that would be a great thing to achieve and something to build on for the future."