The Catalans dominated after Yacine Brahimi had fired Granada into a 16th minute lead, but despite enjoying more than 80 percent possession and having 29 efforts on goal, they failed to find a way past inspired Granada goalkeeper Orestis Karnezis.
Defeat saw Barca slip to third in the table with just five games to play as Real Madrid beat Almeria 4-0 at the Santiago Bernabeu, whilst Atletico Madrid could move four points clear of Martino's men with a win over Getafe .
"We no longer have matters in our own hands, but I couldn't ask for anything more from the players," he said.
"They tried in every way possible. They created plenty of chances, but today it wasn't to be. I can't criticise them for anything apart from obviously not finishing off the chances we had."
Barca have endured a hellish week as they were also dumped out of the Champions League before the semi-finals for the first time in seven years by Atletico in midweek.
The last realistic hope for Martino's men of winning some silverware this season therefore comes when they face Real Madrid in the Copa del Rey final.
However, the Argentine insisted his side will be up for the fight against Real having already beaten Los Blancos twice this season.
"Obviously after the defeats we have had in the Champions League and the league the dressing room feels as if it has let important opportunities go, but the game doesn't depend on the Champions League or La Liga. It is a final and we have to try and win it."
Atletico could also now seal their first title since the 1995/1996 season before they travel to face Barca at the Camp Nou for the sixth time this season on the final day of the campaign.
Martino, though, insisted Barca wouldn't give up the fight to retain their title until it is mathematically beyond them.
"It is clear that I can feel good after the results we have had. However, that also doesn't mean that we won't fight until the end.
"We can't confuse the sadness we feel after a disappointing result with giving up. We will never give up until it is mathematically impossible."
Real will go into the Cup final in much higher sprits as goals from Angel di Maria, Gareth Bale, Isco and Alvaro Morata took them level on points with Atletico at the top.
However, injury problems are mounting for coach Carlo Ancelotti as Sergio Ramos missed Almeria's visit due to a neck injury and joins Cristiano Ronaldo and Marcelo as doubts for the clash against Barca .
"I am confident Ramos will be fit for , he just had a small problem with his neck and (Xabi) Alonso and (Dani) Carvajal who were suspended today will return.
"At the moment I don't know if Ronaldo will play. Marcelo is doing individual work and I don't think he will be fit for ."
Ancelotti admitted he was surprised by Barca's defeat earlier in the day, but doesn't believe it will overly affect their clash at the Mestalla in Valencia.
"I was a little surprised because Barcelona have more quality than Granada, but this is a very dangerous league and at this time of the season every game is very difficult.
"I think Barcelona still think they can win the league. They will fight until the end, which is normal, and I don't think that will change a lot ahead of ."