Juventus' run of home wins in Serie A was ended by a 1-1 draw against Sampdoria after a goal from Manolo Gabbiadini, a player they co-own.
Patrice Evra looked to have ensured the Turin club's extraordinary run of 25 home league wins in a row would continue with his first Juventus goal early on.
But following a switch to 4-3-3, Sampdoria improved after the break and half-time substitute Gabbiadini scored a fine equaliser just six minutes into the second half.
Juventus own 50 per cent rights to the player, but he provided a scoring touch against them to halt an incredible winning sequence, which also opens the door for Roma to close the gap on the champions.
Massimiliano Allegri had seen his side's momentum falter of late.
A six-match winning run was ended by a goalless draw at Fiorentina in their previous league outing before another stalemate against Atletico Madrid on Tuesday secured their place in the last 16 of the UEFA Champions League.
Sinisa Mihajlovic's men meanwhile have forced their way into the fight for a spot in next season's Champions League, and are now unbeaten in six league matches.
The champions started without the suspended Giorgio Chiellini, while Andrea Pirlo was rested following his midweek exertions.
But neither was missed as the hosts were on the front foot from the first whistle with Mihajlovic's men almost immediately pegged back to their 18-yard line.
The tone was set early as a string of dangerous crosses were sent into the Samp box in the first six minutes, Alvaro Morata heading one just wide from six yards.
And any remaining fears of a third straight goalless draw were soon alleviated.
Pirlo's replacement, Claudio Marchisio whipped in an inviting 12th-minute corner, which Evra rose highest to meet with his head and claim his first Juve goal.
It was no less than the league leaders deserved, and with Sampdoria offering little by way of an attacking threat, the hosts eased off slightly and lost some of the pace that had characterised their early play.
The visitors committed more men forward as half-time approached, winning two late corners, but a lack of cutting edge prevented them from truly threatening Gianluigi Buffon's goal.
That improved finish to the first period had given Samp an injection of belief and they equalised soon after the break.
Left-back Vasco Regini started a swift break forward after his goalkeeper Sergio Romero added to his growing collection of saves with a diving stop to deny Roberto Pereyra.
The ball was soon at the feet of Gabbiadini on the right-hand side of the box and the forward cut in to curl a left-footed effort into the far corner.
Juve piled on the pressure in search of a winner, introducing Fernando Llorente to spearhead a more direct approach.
But Romero stood firm and Allegri even had Buffon to thank as he denied another fierce Gabbiadini effort at the other end which almost condemned his side to a first Serie A defeat at Juventus Stadium since January 2013 - when Samp were their opponents.