Luis Suarez headed in the only goal as defending champions Barcelona edged Valencia 1-0 in their Copa del Rey semi-final first leg at a half-full Camp Nou on Thursday.
Barcelona, the record 29-time winners of the tournament, are attempting to become the first team to lift the cup four years in a row since Athletic Bilbao in the 1930s.
But they were forced to labour against a Valencia team missing a trio of key players - Goncalo Guedes, Geoffrey Kondogbia and Ezequiel Garay - through injury.
Barcelona dominated possession but had to wait until the 67th minute for the breakthrough.
Not surprisingly, Lionel Messi was the man who unlocked the Valencia defence before setting up Suarez. The Argentine danced his way into the penalty area before a deft left-footed chip left three defenders out of position and allowed Suarez to score from the edge of six-yard box with a diving header.
Thursday's tight affair was dramatically different to the last time these two teams met at the same stage two years ago when Barcelona won 8-1 on aggregate following a 7-0 win in the first leg.
"We have a small advantage but there's still 90 minutes to play and it'll be a long 90 minutes as Valencia are a very strong when they play at home," said Suarez who has now scored 13 times in the last 11 games.
In Wednesday's first semi-final, little Leganes, who stunned mighty Real Madrid in the quarter-finals, battled back from a goal down to draw 1-1 with Sevilla in the opening leg.
Colombian international Luis Muriel gave Sevilla the lead after 21 minutes, scoring with the aid of a deflection off the post.
But Leganes levelled on the night when Sevilla goalkeeper Sergio Rico blundered trying to keep out a header from Greek defender Dimitrios Siovas.
Leganes, who were playing in the third division five years ago, are in the Copa del Rey semi-finals for the first time in their 90-year history.