With Ronaldo suspended following his red card in last year's final defeat to Atletico Madrid and Bale left in the Spanish capital due to the flu, Real boss Carlo Ancelotti handed starts to young forwards Alvaro Morata and Jese Rodriguez.
However, the Spanish under-21 duo failed to impress as Real failed to find the net for just the second time this season.
And Ancelotti believes the artificial surface at La Murta affected his side's performance.
"The match wasn't that bad. It is true that the artificial pitch didn't help us, we are not used to playing on pitches like that," he said.
"We don't need to be worried about a lack of goals. That is not a problem we normally have."
After a first-half devoid of clear-cut chances, Madrid improved markedly after the break as Isco and Morata both wastefully fired wide when presented with good sights of goal.
Angel di Maria then showed his displeasure at Ancelotti as he stormed down the tunnel when being replaced by Karim Benzema just before the hour mark.
However, even the French international couldn't find the breakthrough as he flashed a shot just wide with his best opening 11 minutes from time.
Madrid will though still be heavy favourites to progress when the two sides meet again for the second-leg at the Santiago Bernabeu on .
Atletico Madrid began their defence of the title with an comfortable 4-0 win away to Sant Andreu.
Goals from Raul Garcia and David Villa either side of an Arda Turan double mean that Atletico can already start planning for the last 16 in January.
"The commitment of the team was very good," said a satisfied Atletico boss Diego Simeone.
"We handled the game very well and the result is obviously a very good one. The more players we have scoring goals the better so it was good to see Raul score again and Arda got two."
Garcia continued his fine scoring form of late with the opener after just 12 minutes before Turan effectively ended the tie as a contest with a second away goal when he tapped home from Manquillo's intelligent cut-back just eight minutes later.
The Turkish international doubled his tally for the afternoon 10 minutes after half-time as he took advantage of some frantic defending to slot home from inside the area.
Simeone had rested top scorer Diego Costa and David Villa from the start, but the Argentine showed no mercy on the lowly Catalans as he introduced his first choice striker partnership with 20 minutes to go.
And Villa had time to grab his 10th goal of the season with classy finish six minutes from time to make it 4-0.