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.
"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."
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."
Barca's first chance came in the 19th minute when Andres Iniesta lifted a pass into Messi's path.
