© AP Photos
The German veteran opened the scoring on 22 minutes as he reacted quickest to tap home after Antonio Candreva's strike from range was parried into the danger zone by Dejan Stojanovic.
Hernanes smashed in a second for the home side, before Klose completed a first-half hat-trick with two goals in three minutes.
The 34-year-old showed no mercy in the second half, rifling in his fourth after meeting a precise cross from Candreva.
Sergio Floccari was then instrumental as he created another chance for the German international, who made no mistake to crash home his fifth and Lazio's sixth.
Lazio coach Petkovic decide to swap Klose for Louis Saha with 20 minutes left, making him the first player to hit five in a single Serie A match since the 1984-85 season.
Bologna were unable to register a response in the closing stages as Lazio ended a run of four games without a win in resounding fashion.