The midfielder, who was on loan at Inter last season, and Jordi Alba scored to maintain Barca’s 100 per cent start to the competition.
Lionel Messi – out with a broken arm – watched from the stands at the Nou Camp as Barca dominated the Group B tie on Wednesday.
Barca remain top of the group ahead of El Clasico on Sunday, with Rafinha ready to face Madrid.
“This result is a great confidence boost for all of us and when Sunday brings the Clasico we’ll be so up for it,” Rafinha told Movistar, with Ernesto Valverde’s side one point clear at the top of LaLiga.
“We are very happy for the match, against a team that was going to make things very difficult for us, we played very well.
“The Champions League is special for us, although the other competitions are also very important.
“But also for the win, for the goal and for the intense motivation a night like this gives me.
“We did very well against a team we knew would cause us difficulties all night. To win like this, Barca had to produce very good football.”
Rafinha volleyed in Luis Suarez’s cross after 32 minutes and Alba wrapped up the win with seven minutes left.
Inter are now three points behind Barca in Group B following their first defeat in the competition this season.
They host Barcelona in two weeks needing to win to ensure they have a better chance of topping the group.
Nerazzurri coach Luciano Spalletti told a post-match press conference: “We didn’t show as much character compared to our first two Champions League games.
“We weren’t courageous enough and the opposition made the most of our attitude. We didn’t do as much as we can.
“We also could’ve scored over the course of the game but they were stronger than us and deserved to win. They play well, passing the ball quickly and thinking fast.
“We came into the match with a bit of hesitancy. We had some issues with passing the ball with pace, therefore, everything became much more difficult.
“We should’ve been more aggressive in winning the ball back and then more precise in possession. You can’t just play on the counter-attack when you come to Camp Nou.”