Messi had earlier Sunday said his farewells to the club he had served for 20 years at a tearful news conference.
Memphis Depay opened the scoring for Barcelona after just three minutes with Martin Braithwaite adding a second goal just before the hour mark from a corner.
Young hope Riqui Puig scored a third in stoppage time with a fine left foot drive.
In Sunday's other high-profile friendly, Real Madrid and AC Milan fought to a 0-0 stalemate.
Spain's La Liga season gets underway on Friday while the Italian Serie A starts on August 22.
