The Catalans had 86 percent of the possession but spurned a number of openings, with Yacine Brahimi's first-half strike the difference between the two sides on Saturday evening.
The result leaves Atletico a point clear at the top of La Liga ahead of a clash with Getafe on Sunday, while Real Madrid will move a point clear of the Blaugrana with victory over Almeria.
Martino said: "Liga lost? It is out of our hands now, of course. But we will keep fighting. I can't blame the players, they kept going, we had the chances but just couldn't finish.
"We'll keep on fighting until the end and of course in the Copa del Rey final on Wednesday as well."
Javier Mascherano partnered Alex Song at center back, with Carles Puyol and Gerard Pique both absent through injury, and the Argentine echoed the sentiments of Martino in backing Barca to bounce back.
"We have to get up now and show we're men," he added. "On Wednesday we cannot fail, we have to give ourselves and the fans some joy.
"We didn't play a bad game today, we worked hard but the ball just didn't want to go in."
- Sports & Recreation
- La Liga
- Real Madrid
- Yacine Brahimi