Barca dominated after the early scare but failed to take advantage and visiting goalkeeper Edwin van der Sar was only seriously tested by substitute Thierry Henry late in the game.
The only non-English side in the semis have been poor in the Spanish league but gave a far more impressive performance against an out-of-sorts United.
The Catalans put the visitors under heavy pressure with Deco driving forward from midfield and feeding the attacking trio of Lionel Messi, Andres Iniesta and Samuel Eto'o.
|"Today I didn't score but no problem, I will score in Manchester."|
Deco and Yaya Toure dominated the midfield and United got little possession of the ball, surrendering it quickly whenever they did get it.
Messi, making his first start since returning from a thigh injury, ran out of steam in the second half and Barca coach Frank Rijkaard sent on youngster Bojan Krkic and then Henry.
The Frenchman almost broke the deadlock with a rasping drive seven minutes from time but van der Sar got his hand to it then stopped a free kick by the former Arsenal player to ensure the game finished in a stalemate.
Barca will feel short-changed that they will not be bringing a goal advantage to Old Trafford for the return leg next week.
"It is not a bad result," said Cameroonian striker Eto'o, who blasted Barca's best chance of the night into the side netting five minutes after half-time.
"We'll see how they play at their place.
"We did not score but we can score over there - if we score once they will have to get two and that will be hard for them."