France striker Thierry Henry grabbed the potentially crucial equaliser when he stooped to head home from less than a metre in the 67th minute after defender Rafael Marquez deflected a Lionel Messi corner towards the far post.
The French champions, whose pressure in the closing stages failed to produce a winner, face a daunting task in the return leg at the Nou Camp in two weeks' time.
Barcelona, who slumped to a shock 2-1 home defeat by city rivals Espanyol at the weekend, rose to the occasion in the second half and it proved too much for Lyon.
"I regret that we didn't profit from our period of dominance in the first half," Lyon coach Claude Puel told reporters.
"In those moments of strength, you have to be able to score a second or third goal. After all our (early) efforts we stood back...But it's a long way from being over."
Barcelona coach Pep Guardiola said he did not panic despite his side's poor first-half performance.
"After the break, we took control of the game and it was much better. We now need to draw the conclusions from this match in order to be ready for the return leg."
Lyon opened the scoring when Lyon captain Juninho's free kick caught the Barca defence napping to sail over the static Valdes and into the net.
BENZEMA THREAT
The Barcelona's defence was again caught off guard by Karim Benzema a minute later but the France striker missed the target from just inside the area.
Although Barca enjoyed most of the possession, Lyon were sharp on the break and showed more aggressiveness.
However, Lyon were quickly reminded that Barca were not to be written off so quickly when Samuel Eto'o whipped in a low shot that crashed off Hugo Lloris's right post on 14 minutes.
Benzema also hit the woodwork in the 27th when he curled a shot onto Valdes's left post.
Messi had the Lyon crowd booing him throughout an ill-tempered first half after he theatrically fell holding his head following a Fabio Grosso challenge.
Barcelona sprung to life after the break and Lyon needed two stunning stops by Lloris to stay ahead.
A Daniel Alves free kick was deflected towards the goal in the 57th minute and Gerard Pique thought he had an equaliser from close range eight minutes later but both times, the French keeper denied Barca.
The visitors found the net, however, when Mexico's Marquez sharply headed Messi's corner on and Henry dived to score at the far post.
