Lionel Messi opened the scoring from the spot shortly after halftime in the first leg of the Champions League last-16 tie, after Martin Demichelis was sent off for bringing him down just inside the penalty area.
Daniel Alves then doubled the advantage at the death, putting Barca firmly in the driving seat ahead of the second leg at Camp Nou in March.
"For 10 minutes during the first half we lost control a little but in the rest of the game we did well," the Argentine coach told reporters.
"We have to remain calm and continue along the same path because there is no time to relax as we must now start thinking about our next game in La Liga.
"We have clear objectives in each tournament. We can play better or we can play worse than tonight but in no way are we going to relax."
Barcelona is back in action on Sunday in a visit to Real Sociedad, as the Blaugrana look to retain their place at the top of La Liga.