Barcelona set a La Liga record as they extended their unbeaten run to 39 games.
The Catalan club were always in control of the match and they took the lead inside 15 minutes through Luis Suarez.
Samuel Umtiti then doubled the advantage six minutes after-half time to all-but secure the win, before Daniel Parejo netted a late consolation penalty.
Coutinho was forced to sit out of Barcelona’s midweek Champions League exit because he is cup tied, but the midfielder was delighted to return to help his side take one giant step towards securing the league title.
“For me, he’s[Messi] the best in the world, it’s an honour to play with him,” he said.
“We have to keep going as a team because we’re in two important competitions.
“We have to look forward, today’s victory was important.
“Even though I couldn’t play in the Champions League, I still wanted us to win it.
“I’m part of this team, nothing can change that.”
“It’s been a difficult week because of the Champions League result.”
Coutinho also explained the changes he has had to make since swapping Liverpool for Barcelona in January.
“I am, little by little, trying to feel better on the pitch,” he added.
“I always say that at Barcelona you play a little differently.
“I have to incorporate that style into my way of playing.”