How United fans would love to see that scoreline after a UEFA Champions league match but unfortunately its only a pre-season tournament.
The match played in front of 68,414 at Levi’s Stadium in Santa Clara, California was Man Utd’s best pre-season victory so far by.
Wayne Rooney’s eighth-minute header from Ashley Young’s corner put United in front.
Jesse Lingard doubled the lead when he swept home Tyler Blackett’s cross after Louis van Gaal had replaced his entire starting XI just past the hour mark.
Rafinha’s splendid volley in the final minute was followed almost immediately by United’s third from Adnan Januzaj as Van Gaal’s team struck on the break.
Victory over the European champions is a welcome sign of progress for Van Gaal – particularly in attack – although Barcelona did hit the woodwork on three occasions, twice through Luis Suarez, who also had a goal disallowed for offside.
United, who have a 100% record from their three US tour games, have only one match of their pre-season campaign remaining, against Paris St-Germain in Chicago on 29 July.