He has urged Lazio, however, to put the result behind them and start afresh in the next game against Borussia Monchengladbach on Thursday night.
"We conceded the first goal without being focused," Gazzetta dello Sport quotes Petkovic as saying. "Then they scored the second goal and it was all over.
"There are no excuses; we are truly sorry for the result and we apologise to everyone.
"We were wrong and I was wrong to deploy a 3-4-3 formation, but now I want to see the club's great character and start over."
Lazio are fourth in Serie A after the result.