Speaking to Sky Italia, Sarri was left frustrated by his players' reactions during the game.
“We'll need to find the explanation for all this over the next few hours," Sarri said.
“My sensations before kick-off were good, as they were during the week. We conceded a stupid goal in the opening minutes that affected us for the whole game.
“Manchester City play fantastic football and I saw an extraordinary team. We had a total blackout."
Sarri also denied claims he deliberately snubbed City boss Pep Guardiola at the final whistle.
“I just didn't see Pep, as at that moment I just wanted to go into the dressing room. Then, as I always do, I went to salute him afterwards."