In a tense encounter at a packed Bernabeu, the first of four clashes between the teams in three competitions in 18 days, Lionel Messi put Barca ahead from the spot in the 53rd minute after Raul Albiol was sent off for a foul on David Villa.
The champions were cruising towards a sixth consecutive victory in the "Clasico" under coach Pep Guardiola when Dani Alves felled Marcelo and the referee awarded another penalty, converted by Cristiano Ronaldo in the 82nd minute.
With Wednesday's King's Cup final and the two-legged Champions League semi-final still to come, Real may take some comfort from the fact they managed to come from behind to snatch a point despite a numerical disadvantage.
Barca will perhaps feel they squandered a chance to bury their rivals in the league title race in front of a television audience of millions as they bid for a repeat of their 2009 treble of domestic league and cup plus Champions League.
"Coming to the Bernabeu and drawing is a very good result," Guardiola told a news conference. "At 1-0 we perhaps should have put more pressure on Real's goal. We'll try to continue in the same vein so we can be champions."
MISSION IMPOSSIBLE
The Catalan club are on 85 points from 32 matches, with Real on 77, and also have a superior head-to-head record thanks to their 5-0 demolition of Real at the Nou Camp in November that would clinch the title if the pair finished level on points.
Guardiola's Real counterpart Jose Mourinho, a former Barca assistant coach who eliminated them from last season's Champions League while in charge at Inter Milan, said Albiol's dismissal had made it impossible to win the match.
"It was a very balanced game when we were playing 11 against 11," he told a news conference.
"Barca is the best team in the world at holding on to the ball," added the Portuguese, who was incensed that Alves was not shown a second yellow card in the penalty incident. "With 11 against 10 they were able to do what they wanted."
Despite needing all three points to reignite their title challenge, Mourinho opted for an unusually defensive lineup, with playmaker Mesut Ozil relegated to the bench and centre-back Pepe deployed as one of three defensive midfielders alongside Xabi Alonso and Sami Khedira.
Barca were content to play the ball around in midfield in the early stages without making much progress towards goal, while the home side looked to catch the visitors on the break.
FIRST CHANCE
Barca's first chance came in the 19th minute when Andres Iniesta lifted a pass into Messi's path.
The World Player of the Year controlled the bouncing ball with his head but goalkeeper Iker Casillas blocked his attempted lob with relative ease.
Real were lucky not to concede a penalty shortly afterwards when Casillas appeared to bring down his Spain team-mate Villa in the penalty area without making contactn with the ball.
