Lacklustre Juventus needed a Cristiano Ronaldo penalty to salvage a 2-2 home draw with Sassuolo that left the door ajar for Serie A title rivals Inter.
Maurizio Sarri's men were set to pay a hefty price for a poor performance until Paulo Dybala appeared off the bench and won a 68th-minute spot-kick, which Ronaldo duly converted.
Leonardo Bonucci had fired Juve into a 20th-minute lead but an almost immediate response from Jeremie Boga seem to send panicked shivers through the home side.
Francesco Caputo capitalised on dual defensive blunders to give Sassuolo the lead and, though Juve steadied enough to pinch a point, the result would have been appreciated by Inter, who had SPAL at home later on Sunday.
Coach Sarri heeded Emre Can's public plea for a start and the midfielder's first major act was to miscue a straightforward finish.
Gonzalo Higuain stabbed a tougher chance past the post before captain Bonucci set the example.
The centre-back's ambitious drive whistled past teenage debutant Stefano Turati in the Sassuolo goal and gave Juve a lead that lasted barely two minutes.
The equaliser arrived in style as Boga produced a divine dink over the onrushing Gianluigi Buffon after Caputo's pass had nutmegged Alex Sandro.
Italy great Buffon was beaten again within two minutes of the restart, this time from an entirely less glamorous finish.
Matthijs de Ligt's rash clearance was sent back into the box and Caputo's tame attempt squirmed through a red-faced Buffon.
Turati proved more assured as he acrobatically parried Ronaldo's free-kick, before Higuain and Can squandered gilt-edged opportunities.
Ronaldo had a goal correctly disallowed for offside but was not to be denied from the spot, the 34-year-old confidently converting after Filippo Romagna brought down Dybala.
Juve looked likely to go on and snatch a winner, but a Dybala shot that drew an excellent save from Turati and a Ronaldo header that looped wide proved the closest they came.
What does it mean? Juve's gift to Inter
It could have been worse for the Bianconeri but a third draw in 14 league fixtures gave Inter a chance to edge ahead in the battle for the Scudetto. Perhaps more concerning for Sarri will be just how often talented players committed sloppy errors.
Teenager Turati outshines shaky Buffon
In stark opposition to the calamitous showing from veteran Buffon was an 18-year-old first-timer who shone for Sassuolo.
Turati, thrown in at the deep end due to Andrea Consigli's absence, made seven saves in total, most of them of a high quality.
Can wastes rare starting chance
From Federico Bernardeschi to Buffon, De Ligt and even Ronaldo, there were candidates aplenty to be judged Juve's least impressive performer. But midfielder Can, so vocal about his lack of opportunities, was effectively a handicap as he fluffed two golden chances to score and was careless on the ball.
Key Opta stats
- Bonucci and Real Madrid's Sergio Ramos are the only defenders to have scored two or more goals in each of the last seven campaigns in the top five European Leagues.
- Ronaldo has scored his last eight goals for Juventus in home matches.
- This was the first occasion that Sassuolo have picked up a point away from home against Juventus in Serie A - and the first time this season that Juventus have not won at the Allianz Stadium.
- Turati became the first goalkeeper born in 2000 to play in Serie A.
Juventus will have to improve away to high-flying Lazio next Saturday, while Sassuolo host Perugia in the Coppa Italia fourth round before a weekend meeting with Cagliari.