But Napoli hit back with Mario Rui lofting a ball for Giovanni Pablo Simeone to nod home for a 78th minute winner.
The result means Napoli are top with 17 points ahead of Udinese who beat Inter Milan 3-1 on Sunday on goal difference, while champions Milan are fifth with 14 points.
Pioli’s side had 22-9 shots but only managed five on target, leaving the Rossoneri boss frustrated.
“I am not satisfied at all and neither should my players be,” Pioli told DAZN. “We only scored one goal, which isnt enough for all that we created.
“It’s disappointing, because nights can happen when the opponents play better, but in this case we really shouldn’t have lost.
“I hope we will learn from this to be more clinical in front of goal, because we did everything right except for errors and a lack of determination in both penalty areas.
“I might come here and say I was very happy because we played better than Napoli and created lots of chances, but seeing as we were the only side unbeaten in Europe’s top five leagues for 22 rounds, longer than Bayern Munich, Manchester City and Real Madrid, it’s a shame to lose it with a performance like that.”
Napoli boss Luciano Spalletti was suspended for the game, with assistant Marco Domenichini taking charge on the touchline and with media duties post-game.
He moved to reject hype around Napoli, when asked if there’s any better squads than theirs in Serie A.
“There must be,” he said. “We just do our best every weekend and will slowly see what happens.
“We’re a young team with many new players and theres still a lot of work to be done.”