Martino's side struggled to hit top form in the Catalan derby, but a late penalty from the Argentine forward secured all the points for the La Liga champions.
"With Messi on the pitch the story almost always ends the same way," Martino told reporters.
"Winning here is important because it was a derby. You always have to win these matches, so we value the victory very much.
"All of the remaining games are very difficult. They are seven cup finals."
Barcelona are currently one point behind league leaders Atletico Madrid in La Liga.