Goals from Dani Parejo, Pablo Piatti and Paco Alcacer inflicted a rare home defeat on the champions, who had previously won their last 25 league outings on home soil.
The defeat means Barca's 59-week stay at the top of La Liga is likely to come to an end with title rivals Atletico and Real Madrid in action on Sunday against Real sociedad and Athletic Bilbao respectively.
And Martino believes his team are playing in "a different league" after Saturday's loss, which will see them hoping to make ground on their rivals for the first time under his stewardship.
He said: "All the options are intact but now we begin to play a different league to what we have done so far.
"We must move forward. Next week we have two very difficult games against Real Sociedad and Sevilla.
"Every time we lose a game we play, we care.
"And it's much more in the league, where losing a game means losing a piece of the championship.
"But we will fight without any doubt and try to fix our mistakes."
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