Edy Reja admits Lazio “paid a heavy price for a naive error,” as a draw slipped from their grasp at the 94th minute.
Luis Cavanda was picked to mark Milos Krasic, but the Serb got to the by-line for the winning Juventus goal.
“Cavanda is young and he didn't realise you mustn't give Krasic space to cut inside,” said Reja of their 2-1 defeat.
“We paid a heavy price for a naive error. It's a real shame, as the game was effectively over by then. We were there, but towards the end couldn't keep hold of the ball.
“Of course there are regrets when you lose a match with five seconds to go. Now it will become difficult to rediscover the right spirit.
“At least we proved again this evening that we can challenge Juventus on level terms, even if it wasn't our best performance.”
The result means Lazio are caught in second place by Juve and Napoli.