Martino started with former Arsenal midfielder Alex Song in an unfamiliar role in a back three alongside Gerard Pique and Marc Bartra.

Song endured a torrid time as his own-goal put Sociedad in front before two goals in five minutes just before the hour mark from Antoine Griezmann and David Zurutuza rendered Lionel Messi's equaliser meaningless.

"Losing and ceding ground in the league always hurts, but we will have another chance next weekend and we will continue to fight until the end," said Martino.

"The opponent played very well, they were better than us. The lesson we learned was that our response didn't match up to what was expected of us today.

"The idea was, thinking a bit about (Carlos) Vela and Griezmann as two forwards, to play with three at the back with Busquets in front and the two full-backs pushing forward.

"In the end it was the positioning of (Sergio) Canales that caused us problems because they ended up in a diamond and he was running off the back of Busquets."

Despite a morale boosting 2-0 win over Manchester City in first leg of their Champions League last-16 tie on Tuesday, Martino made six changes to the side which started at the Etihad.

Neymar came into the side for his first start in a month and Martino admitted that also dropping Cesc Fabregas and Xavi to accomodate the Brazilian proved mistaken.

"We did as we have always done in rotating the squad so that all the players feel involved.

"Obviously results depend on whether the rotations are seen as a good and healthy thing or not.

"We felt like we needed to look for more penetration. That is why we played an extra forward, I probably read what we needed for this game wrongly."

Martino's poor evening was rounded off by the fact he had to watch the second period from the stands as he was sent-off at half-time.

However, the Argentine refused to comment on what exactly caused him to be banished from the technical area.

"Respecting my sending off, there is nothing to say. The referee took the decision he did and that is all."

Defender Gerard Pique also recognised that the lack of Xavi and Fabregas meant Barca sacrificed their usual grip on possession.

"We didn't feel comfortable and we didn't have possession, which is our strength. That allowed then to create chances," he said.

"Now we have a week to rest and reflect on why things didn't go well. It is not worrying, we just have to continue onto the next game."

Real Madrid now lead Barcelona after both sides have played the same number of games for the first time this season as they beat Elche 3-0 at the Santiago Bernabeu earlier on Saturday.

Barca could even end the weekend in third place should Atletico Madrid avoid defeat away to Osasuna on Sunday.