Razvan Marin lashed home the 88th-minute leveller to give Cagliari a point at the Allianz Stadium after Roberto Piccoli was clumsily brought down by Douglas Luiz, who also gave one away in Wednesday's thrilling Champions League win at Leipzig.
Romania midfielder Marin's arrowed penalty levelled Dusan Vlahovic's 15th-minute spot-kick and moved Cagliari up to 15th, a point above the relegation zone.
It was the first goal conceded by Juve in Serie A this season and left Thiago Motta's side three points behind league leaders Napoli after seven fixtures.
"We took out foot off the pedal after our goal, and we can't do that. We need to keep attacking, and attack well," said Motta.
"We created a few opportunities but there was always the feeling that Cagliari could get back into the game. What happened today is all our own fault."
Cagliari could have even snatched a last-gasp win as Adam Obert thumped the post in the fifth minute of stoppage time, with Juve down to 10 men following Francisco Conceicao's sending off almost immediately after Marin's equaliser.
Conceicao picked up a second booking after trying to win Juve's second penalty of the game in a frantic finish to a match which had largely been a drab affair before Luiz was penalised for his challenge following a VAR check.
"I'm pleased to get a point at Juve, it was hard because I had the whole stadium whistling me but I managed to keep my concentration," said Marin.
Juventus, who were missing Nico Gonzalez, Arkadiusz Milik, Timothy Weah and Gleison Bremer who suffered a serious knee injury at Leipzig, would have almost certainly had the full three points had Vlahovic not wasted a huge chance in the 78th minute.
Serbia striker Vlahovic, who is on five Serie A goals for the season, somehow shot wide on the rebound after Douglas Luiz's shot was parried by Simone Scuffet.
His opener was controversial as the penalty was awarded for Cagliari defender Sebastiano Luperto's fingers grazing the ball as he engaged in an aerial tussle with Federico Gatti.
The spot-kick was given after a VAR check as Luperto's arm was high in the air when he touched the ball, but he was landing from his jump and had Gatti leaning on his shoulder while two other players also battled for the ball.
AC Milan can move above both champions Inter and Juve with a win at Fiorentina in the day's final fixture.
