Frattesi, on for Fisayo Dele-Bashiru just five minutes earlier, converted a Boulaye Dia flick to settle a tightly contested affair at the Renato Dall'Ara, handing Gennaro Gattuso victory in his first competitive match in charge of Lazio.
Gattuso was pleased with his side's overall control of the ball.
"Today we were very good in possession. I'm happy for the group of lads I'm coaching because they're giving me everything. I don't know where we'll end up, but for now the objective is to become a team and suffer as little as possible. Mandas was heavily criticised and instead today he was one of our best players. We need to improve in the final 20 metres, because we get there well but we make the wrong choices," he said.
The Lazio head coach also praised Alessio Romagnoli's decision to remain at the club despite fitness concerns.
"Alessio has tendon problems. This week he didn't train twice and then gritted his teeth to take part in the warm-up session. He's a good lad, I had him at Milan. We'll see what happens. Frattesi deserves nothing but praise too — another player in his position wouldn't have come here given Lazio's difficulties," Gattuso said, explaining that the midfielder started on the bench because he had only completed six training sessions with the squad and was not yet ready to be relied upon positionally.
Gattuso also moved to clarify speculation around a reported rift with the club hierarchy following last week's Coppa Italia exit to Mantova.
"I haven't argued with anyone. The defeat was painful and there was disappointment. I put my hands up and apologised. Some of you wrote that I argued with Fabiani and Lotito, but none of that is true," he said, adding that Adam Marusic would undergo tests the following day on a hamstring issue.
For Bologna, head coach Domenico Tedesco was left to rue missed chances on his own competitive bow.
"Lazio scored during our best spell. We wanted to change our attacking approach regardless of the goal we conceded. We wanted to put in a good performance but unfortunately we didn't manage it. We're a young team and we need to grow — this defeat will help us take a step forward," Tedesco said.
Asked about his reluctance to start Jonathan Rowe, who remained on the bench amid transfer speculation, Tedesco insisted the winger remained central to his plans.
"He's an important player for us, there's a good battle for that position with Cambiaghi, who's had an excellent pre-season. We're spoilt for choice out wide, but Rowe is fundamental," he said, adding that fitness concerns were also a factor for his forward options.
"Piccoli did well before fading, with the heat and workload for a player of his build having an effect. Dovbyk is training partly with the group and doing extra work to catch up quickly — five months out is not easy."