In a fractious Europa League encounter in Greece, the Biancocelesti took the lead courtesy of Giorgos Seitaridis' comical own goal in the first half, but Toche denied the Italians all three points at the death.
Petkovic opted to rest his star striker Miroslav Klose, who has been instrumental in Lazio's strong start to the Serie A campaign, but pledged to unleash the rested German at the Stadio Artemio Franchi.
The Bosnian coach said: "Klose is a professional and at the last moment I decided not to use him, so that he would be in good condition for Sunday.
"I hope to have everybody at my disposal.
"We could and should have done better. Unfortunately we're not yet mature enough, and we have to improve.
"Our killer instinct went missing. We had a flurry of chances to kill the game off, but we gave too much away to our opponents.
"We have to be more crafty and we have to play for the whole 90 minutes.
"I even rested some important players, those who've been playing a lot, but those I brought in didn't make the most of taking someone else's spot."
There was a break in play on Thursday night as Greek police used tear gas to quell scuffles outside the Olympic Stadium, with Petkovic left bemused.
"At one point my eyes started burning and I wasn't sure why," the Bosnian added. "Our keeper (Albano Bizzarri) was calling for a break because he couldn't see properly, but we didn't really know what was going on."
Viola boss Vincenzo Montella has also issued a stern message of "must try harder" to his players following Sunday's disappointing draw at Chievo.
The Tuscan outfit have won three times at home this season and their young boss is eager to make it four and halve the current six-point advantage held by tomorrow's opponents.
"We won't talk about objectives now," said Montella. "But it's clear we're not giving our all."
The participation of Mounir El Hamdaoui is in doubt after the Moroccan striker took a hard knock during training this week.