The Biancoceleste were held to a 1-1 draw by 10-man Samp last weekend, much to Petkovic's frustration.
"We did not read the match properly," he said. "We were not ourselves and we never came to life.
"We should have played the match differently but we approached it the wrong way.
"Samp showed more hunger even when they were a man down than we did throughout the game.
"We are a long way off the consistency we're looking for.
"We need to improve.
"Our performance at Sampdoria was below par and I expect a response from my players on Monday."
Lazio have not come out triumphant in Serie A since beating Cagliari 2-0 on October 25 and are eighth in the table.
Fortunately for Lazio, things are looking better in the Europa League.
The Romans secured their place in the last 32 of the competition with a 2-0 triumph at Legia Warsaw on Thursday.
Rivals Napoli hope to leave behind them a disappointing week.
Rafa Benitez's men lost 1-0 to Parma last weekend as they went down to their second straight defeat in the league before losing 3-1 at Borussia Dortmund in Wednesday's Champions League game.
The defeat in Germany complicated Napoli's hopes of reaching the knock-out round of the Champions League.
Napoli must now beat pool leaders Arsenal at home on December 5 by a 3-0 margin or hope that Borussia drop points at winless Marseille in the last group game to join the Londoners in the last 16 of the competition.
"We must put this loss behind us and concentrating on getting back on track in Serie A," Benitez said.
Napoli are third in the standings and hold the last Champions League qualifying spot.
Napoli will be hoping to recover attacking midfielder Marek Hamsik, who missed the midweek European game with a foot injury.