Juventus remain top of Serie A on 56 points but could see their lead over second-placed Roma cut to six points if the Giallorossi account for Verona in Sunday's early game.
Juventus were looking for their 13th successive win since losing 4-2 to Fiorentina on 20 October.
But their bid suffered a blow before the half hour when Buffon, who had already almost gifted Miroslav Klose a free scoring chance, saw red for hauling the German striker down on the six-yard line.
Buffon made way for number two 'keeper Marco Storari, with Ghanaian midfielder Kwadwo Asamoah forced off to leave Juve a man down.
It was Buffon's first Serie A dismissal since February 2011, against Lecce, and the visitors were 1-0 down when Antonio Candreva sent Storari the wrong way from the spot in the 27th minute.
Juve coach Antonio Conte told Sky Sport Italia: "We were looking for the win, whether we were at full strength or not. Our winning attitude remained intact even with the setback of our keeper's sending off.
"I was happy with the team's reaction, it's in times like these that their character as men, and not just as players, comes to the fore."
Lazio had claims for another penalty waved away just before the interval after the ball clearly came off the arm of defender Leonardo Bonucci as he challenged deep in his own area.
Both sides created a series of chances in a lively second half but Juve overcame their disadvantage to pull level on the hour after a well-worked move starting with Carlos Tevez.
The Argentinian striker held off his marker on the edge of the area to send Stephan Lichsteiner through on the right, with Fernando Llorente's glancing header from the Swiss midfielder's cross creeping inside Etrit Berisha's far post.
Lazio coach Edoardo Reja said: "We played a great game, despite a disappointing start due to Juve's pressing early on."
Raul Albiol scored his maiden goal for Napoli but a week after settling for a 2-2 draw away to Bologna, their slim title hopes were dented again.
Napoli remain third and are still 12 points behind Antonio Conte's men.
"It's not easy to play against a side that closes the game down like that but we have to rediscover the intensity that we had at the start of the season," the Spaniard said.
Napoli were stunned inside 20 minutes when Gennaro Sardo finished off a one-two with Cyril Theareau to smash a stunning drive past Rafael Cabral and into the top corner.
The hosts tried to hit back but Gonzalo Higuain somehow missed the target from barely a yard out after Jose Callejon's angled shot, which had beaten Christian Puggioni, found him unmarked at the back post.
Dries Mertens' effort from a tight angle then found the outside of the post, the first of three efforts to hit the woodwork with Mertens' free-kick hitting the upright and late substitute Lorenzo Insigne's rising drive skimming off the crossbar.
With just two minutes remaining Albiol spared Napoli's blushes when he pounced from a corner to squeeze a deflected shot past Puggioni at his near post.
Roma, second and eight points behind Juve, are away to Verona on Sunday while Napoli's fifth draw of the campaign has given a boost to Fiorentina, who are four points adrift of them before Sunday's game against Genoa.