Luis Suarez's 82nd-minute header denied Atletico Madrid a first LaLiga win over Barcelona in seven years.
Barca's perfect start to the league campaign ended with a 1-1 draw in the capital, though they were on course to leave empty-handed when Saul Niguez fired home after 21 minutes.
Atleti have knocked Barcelona out of the Champions League twice in recent years but a success over them in their domestic division has proved elusive since Valentine's Day 2010, and so it proved again as Suarez rose at the back post to head in substitute Sergi Roberto's cross.
The visitors nearly went ahead inside 30 seconds, when Saul made his first key contribution in front of his own goal.
Lionel Messi cut in off the right flank, played a one-two with Suarez and shrugged off Filipe Luis only for Saul to poke the ball behind as Barcelona's key man prepared to pull the trigger.
Atleti woke up and dominated the rest of the first period, with Marc-Andre ter Stegen brilliantly denying Antoine Griezmann on two occasions.
The first was a fine one-handed save at his near post after Andres Iniesta gave the ball and Ter Stegen thwarted Griezmann again, this time with his left leg, after the Frenchman had driven into the box by nutmegging Gerard Pique.
Ter Stegen would be beaten in the 21st minute when Saul unleashed an unstoppable attempt beyond him from 25 yards. The 22-year-old drifted off Ivan Rakitic to collect Yannick Carrasco's pass and fired a right-footed shot that swerved past Ter Stegen and into the net.
Suarez, who had left for international duty having scored just twice, did not initially seem buoyed by his midweek double for Uruguay as he pulled out of a header from a Messi free kick when unmarked.
This was an Atleti side who had conceded just once in the league since August and their defensive resolve was evident when Stefan Savic blocked a Suarez shot just before the break.
The former Liverpool forward had the best chance of the early second-half exchanges when he breezed beyond Diego Godin and rifled in a try that Jan Oblak was behind.
Home fans inside the Wanda Metropolitano feared the worst when Messi won a free kick 25 yards out. However, Barcelona's No. 10, so often Atleti's nemesis, curled his dead-ball effort onto the outside of the post.
Suarez wanted a set piece inside the box when the ball may have come up and struck Savic's arm, though the referee was disinterested and the replays were inconclusive.
Messi fired just wide as Barcelona's confidence grew and Suarez nearly levelled when free inside the box only for a poor first touch to precede a weak attempt at Oblak.
Yet opportunities continued to come his way and Suarez peeled away from Savic to reach Roberto's cross and nod down past Oblak.
Andre Gomes almost reached Suarez again and the final kick of the game was Messi's free kick from the edge of the box which Oblak managed to hold on to.