Pep Guardiola admitted Barcelona were well below their best in their surprise 2-0 defeat at home to newly-promoted outfit Hercules on Saturday.

Barca dominated proceedings early on, but went behind to a goal from Paraguay forward Nelson Haedo Valdez after 26 minutes.

The South American, making his debut for the visitors, added a brilliant second on the hour and there was no way back for Barcelona.

"I congratulate Hercules. They came here and played well. They made it difficult for us and they got their reward," Guardiola said.

But the Barca coach admits his side produced an off-colour performance in their first home match of the Primera Division campaign.

"We lacked our usual fluidity. There are so many details we can improve on. We'll have a look at it and try to overcome it. We have overcome so many things since I've been here and we will again," he said.

Barca face Panathinaikos in the Champions League on Tuesday and with that match in mind, Guardiola decided to rest several of his first-choice players.

Nevertheless, the Barca coach said the side he fielded - which featured the likes of Lionel Messi, Andres Iniesta, David Villa and debutant Javier Mascherano - was good enough to win the match.

"I picked a team to win the game. These are all Barca players and they are all top-level footballers. It was a good enough team, but we lacked fluidity," he said.

Mascherano was replaced at half-time by Xavi as Barca looked to adopt a more attacking approach in the second period, but Guardiola was pleased with his new player.

"Mascherano played really well - I just felt we needed to change things," he said.

Many of Barcelona's players had just returned from an international friendly in Buenos Aires, where Spain lost 4-1 to Argentina on Tuesday night.

Guardiola said that match was far from ideal preparation, but refused to blame tiredness for the defeat.

"Ideally, you would want the players to travel in Europe, not to South America and other places, but these things are beyond our control," he said.

"I don't know if it was a question of tiredness. There was no talk of physical problems when we beat Racing Santander 3-0 or when we beat Sevilla 4-0 in the Supercopa.

"We still created enough chances to win the game. Today we didn't take our chances, but we had a lot of opportunities."

Barca now switch their attentions to the Champions League fixture on Tuesday and Guardiola said they will be ready for the game against Panathinaikos.

"It's another big match and we'll have to pick ourselves up like we have done before - there is no need for alarm," he said.

Mascherano, meanwhile, was disappointed to lose his first match as a Barca player.

"It was a great surprise to start the match and my team-mates helped me a lot. I felt comfortable, but it's a bitter feeling to lose. There's not much more I can say - Hercules played a virtually perfect game," he said after the match.

Hercules coach Esteban Vigo was naturally thrilled with the result.

"It's only three points, but it's a historic victory," he said.

"At the moment I feel tremendous joy and this will be on my coach's CV forever, but I have to remember that we still haven't achieved anything and on Monday all of this won't exist."