MADRID (REUTERS) - Barcelona conceded a surprise early goal but a double from Pedro Rodriguez helped them fight back to secure a 4-1 victory at third-tier Cartagena in their King's Cup last 32, first leg on Friday.

Coming into the match on the back of consecutive defeats in the Champions League and La Liga, Barca's first losses of the season, coach Gerardo Martino deployed most of the first-choice players available to him despite their lowly opposition.

However, it was the home side who struck first at their modest Cartagonova stadium on the south coast when forward Fernando raced clear in the 16th minute and finished low past Jose Manuel Pinto.

The goal seemed to shake Barca, who were missing a slew of injured players including Lionel Messi, Xavi Hernandez and Andres Iniesta, from their lethargy and they threatened several times before Cesc Fabregas sent Pedro through and he shot into the corner.

A superbly-executed Fabregas volley from Adriano's cross made it 2-1 two minutes before half time and Barca squandered several clear chances before Pedro scored his second of the night in the 76th minute from an Alexis Sanchez assist.

Teenage substitute Jean Marie Dongou, from Barca's B team, added a fourth in the 90th minute when he tapped into an empty net after another Pedro effort flew back off a post.

The return leg is at the Nou Camp on Dec 17.