Nearly three weeks after his 160-million-euro ($194 million) move from Liverpool, the Brazilian midfielder replaced Andres Iniesta with 22 minutes remaining in the second half on Thursday.
Luis Suarez and Lionel Messi scored as Barcelona beat Espanyol 2-0 to reach the semi-finals as the holders overturned a 1-0 deficit from the first leg.
A thigh injury had delayed Coutinho’s Barcelona debut but he showed no signs of the problem on Thursday.
“It was a very special night for me and it’s one I’ll never forget,” he said.
“All the supporters and all the players gave me a good welcome and they helped me a lot. I was a bit nervous and anxious but they helped to calm me down and I was able to get into the game.
“I’m very happy to have had my first minutes of action for the club and I’m excited about the reception I received.”
Coutinho is expected to be involved when Barca host Alaves in La Liga on Sunday.
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