Luis Suarez headed the only goal of the game to give Barcelona a slender first-leg advantage in their Copa del Rey semi-final with Valencia.
Barca are seeking to win the Spanish cup competition for a fourth-straight season and dominated at the Nou Camp.
Suarez and Ivan Rakitic wasted first-half chances, while Lionel Messi hit the side-netting after the break.
But Messi’s fine cross found Suarez at the back post on 67 minutes to tee up his 19th club goal of the season.
The second leg will be played in Valencia on 8 February, with Sevilla and Leganes level at 1-1 after the first leg of the other semi-final.
Barca are heavy favourites to win the competition for a 30th time, a success which would likely seal a domestic double given their 11-point lead at the top of La Liga.
Valencia – third in La Liga – had less than 30% of possession at the Nou Camp, where the home side brought January signing Philippe Coutinho off the bench shortly before the hour mark.
At the death, Valencia substitute Santi Mina wasted a clear chance as he headed over the bar.
His miss means Marcelino’s side must come from behind on home turf, where they have not bettered Barcelona since a 3-2 win in this competition back in 2008.