Patrice Evra looked to have put the Turin club on the way to a remarkable 26th consecutive home league win with his first Juventus goal during the early exchanges.
But after a change to 4-3-3, Sampdoria mounted a response after the break and half-time substitute Manolo Gabbiadini - a player co-owned by Juve - scored a fine leveller just six minutes into the second period.
Juventus own 50 per cent of the player's economic rights, but he provided a scoring touch against them to halt an incredible winning sequence, which also means Roma end the weekend just a point behind.
Rudi Garcia's men beat Genoa 1-0 on the road to end their hosts' nine-match unbeaten run in Serie A and close in on Juve.
Genoa goalkeeper Mattia Perin received his marching orders with 29 minutes gone after bringing Radja Nainggolan down in the area, but Adem Ljajic saw his spot-kick saved by replacement Eugenio Lamanna.
Nevertheless, Roma ultimately secured all three points just before the break, Nainggolan netting an acrobatic volley from the edge of the area, leaving Genoa fifth and Garcia's side on 35 points.
Napoli missed the chance to go third in the table as they were beaten 2-0 at San Siro by Milan, who moved level on 24 points with their visitors.
Goals from Jeremy Menez and Giacomo Bonaventura at the start of either half ultimately proved decisive as Milan ended Napoli's 11-match unbeaten run in Italy's top flight.
Rafael Benitez's men saw numerous chances go begging, with Jose Callejon and Gonzalo Higuain particularly culpable, and Milan held on for a morale-boosting win.
Fiorentina moved themselves to within touching distance of the European places with a fine 4-1 win at struggling Cesena, while Verona beat hosts Udinese 2-1 to move five points clear of the drop zone.
Parma - who have been hit with a one-point deduction and €5,000 fine for financial mismanagement - and Cagliari both remain in the bottom three after playing out a 0-0 draw.
