Manchester United lead Barcelona 1-0 at half time thanks to a header from captain Wayne Rooney.
The European champions made a fast start and almost took the lead immediately as Luis Suarez hit the post with a free kick, while Sergio Roberto burst through United's defence and was denied by David de Gea.
Louis van Gaal's side took a surprise lead one minute later as Ashley Young's corner was headed in by Rooney from a few yards out.
The former Premier League champions continued to cause problems on the counter-attack, as Rooney headed over the bar before Young's curled effort forced a diving save from Marc-Andre ter Stegen.
Barca dominated possession and looked dangerous throughout the half, but they continued to look vulnerable at the back as Matteo Darmian set up Rooney, but his shot in the box was blocked.
Luis Enrique's side were reduced to half chances as Sergio Busquets sent a header straight at De Gea from a corner, until Suarez hit the post for a second time with a bending shot.
