Sergio Ramos' 90th-minute header secured a 1-1 draw for Madrid in Saturday's Clasico at Camp Nou to preserve their unbeaten league run and their advantage at the top of the table.
A Madrid win would have opened up a nine-point deficit - only Louis van Gaal's Barca in 1998-99 have won LaLiga from so far back.
Roberto felt Barca deserved to win the match but is fully confident that they will haul in Zinedine Zidane's side if they keep their commitment levels high.
"We deserved to win against Madrid," he told a news conference before Barca's Champions League clash with Borussia Monchengladbach. "We had chances, but against Real Madrid you know that these things can happen.
"You can never relax against them because they score a lot of goals in the final few minutes. Ramos is especially dangerous. We were unlucky that they didn't score until the end, but we're not thinking about it now.
"We could have cut the gap on Madrid, but I don't think that the points difference is that big and if we give 100 percent, we will cut the gap."
The Spain international dismissed suggestions that a drop in form from Barca's midfield has played a major role in an inconsistent run in which they have won only two of their last seven matches in all competitions.
"We have a complete midfield, players who are at a great level," he said. "Maybe we are not playing as well as we can, but that's not the midfield's fault, it's a team issue. We have to keep playing hard together and we'll win titles with the work of the team."
The 24-year-old is eager to sharpen up his own defensive form and hopes that Barca can gain a morale-boosting win in their Champions League dead rubber against Gladbach on Tuesday.
"Things are going well for me," he said. "There are always things to improve - you never do anything perfectly. I can always play better but I'm happy with my form, I'm helping the team a lot.
"You're almost always attacking with Barca and I have to improve my defensive aspects.
"The game is important for us to keep improving, to take some confidence into the next league game and to change the dynamic of the team after three draws in a row."
Barca have already claimed top spot in Group C ahead of the visit of the Bundesliga side.