Juventus failed to atone for their midweek Champions League exit, falling to a 3-1 Serie A defeat at Bari on Saturday.
Bari, who moved up to fifth, took an early lead through Riccardo Meggiorini's deflected half-volley but David Trezeguet tapped in the rebound from a Diego shot to level on 23 minutes.
Paulo Barreto restored Bari's lead from the penalty spot just before halftime but Juve missed a spot-kick of their own when Diego blazed over on 68 minutes.
Bari's former Juventus midfielder Sergio Almiron sealed the win with a piledriver nine minutes from time.
Juve remain third, five points behind leaders Inter Milan, and the defeat will increase the pressure on coach Ciro Ferrara after Tuesday's 4-1 home defeat by Bayern Munich which ended their Champions League hopes at the group stage.
Ferrara's men, who had hoped to have ended an indifferent spell with a 2-1 win over Inter last weekend, were a little unlucky as they created a string of chances they could not put away.
"Obviously the last few days have not been tranquil," Ferrara told Sky television.
"Today it's difficult to find an explanation, honestly. Today was particular. We could have been out there much longer and the ball would never have gone in.
"When my players deserve it, I criticise them. But I don't feel that I can say anything today. The defeat is hard to digest but today I saw what I hadn't seen in the lads' eyes for some time."
Mariano Bogliacino headed an equaliser deep into stoppage time to earn Napoli a 3-3 draw at Cagliari in a thriller earlier on Saturday.
Brazilian Jeda looked to have completed a remarkable comeback for Cagliari when he nodded home in the 90th minute after late goals by Joaquin Larrivey and Alessandro Matri had wiped out Napoli's two-goal lead.
The visitors were well in charge for most of the match, with Ezequiel Lavezzi driving into the far corner in the 22nd minute and Michele Pazienza firing in their second in the 65th.
Lavezzi was sent off shortly before Bogliacino found the net for blasting the ball at Cagliari coach Massimiliano Allegri, sparking a fracas.
Napoli are nineth in the standings, two places ahead of Cagliari.
Inter visit Atalanta on Sunday while second-placed AC Milan host Palermo.