The Biancocelesti twice found themselves two goals down in the match, and needed a late brace from Sergio Floccari to salvage a point.
"We dominated the game but we made too many avoidable mistakes. There are lots of positives for us though because this was a Lazio that believed until the end," Petkovic told Sky Sports News.
"We could've won. We played well and I am pleased. The boys were good, they worked until the very end and kept creating opportunities."
The result leaves Lazio at the top of Group J with four points from their two matches.