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.
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