Barcelona are in pole position to reach a fifth consecutive Copa del Rey final after Luis Suarez's winner saw off Valencia 1-0 at the Nou Camp.
The former Liverpool striker finally made Barca's dominance count in the 67th minute of the semifinal first leg.
Valencia were hammered 7-0 in this fixture last season, a game which former England defender Gary Neville was in charge for, but produced a spirited performance this time around to ensure they head into the return leg within touching distance.
The visitors, currently third in La Liga, were on the back foot from the off as Barca, winners of this competition in the last three years, took control.
The warning signs were there from the third minute when Lionel Messi jinked past a couple of defenders and fired wide.
Aleix Vidal and Suarez were also both off target before Sergi Roberto was fortunate to stay on the field.
The Spaniard received only a yellow card for a high tackle on Andreas Pereira in the 35th minute.
Suarez was a constant nuisance for the Valencia defence and almost broke the deadlock, just narrowly failing to get a touch to Andres Iniesta's ball across the face of the box.
Valencia were struggling to get out of their half and when they did, Martin Montoya smashed a half-volley wide from the edge of the box on the stroke of half-time.
Marcelino's side regrouped at half-time and started to come into the game as Daniel Parejo shot straight at Jasper Cillessen.
But Barca finally got the goal their play deserved when Suarez headed in Messi's cross at the back post.
Former Arsenal midfielder Francis Coquelin tried his luck from distance but his effort landed on the top of Cillessen's net.
Barca's record signing Philipe Coutinho, a 58th-minute substitute, could not beat Jaume Domenech with a curling effort which was comfortable for the goalkeeper.
Another replacement, Paco Alcacer, stung the palms of Juame as Barca searched for a second goal to make the tie comfortable.
Juame was tested again, this time by Messi, before Valencia nearly grabbed an equaliser.
Substitute Santi Mina wasted a great chance as he headed over at the death.