Messi converted the penalty in the 54th minute after fellow Argentinian Martin Demichelis was judged to have fouled him and was sent off.

Alves, who had been a constant threat throughout the game, all but sealed Barcelona's place in the last eight with a sweetly taken goal in the final minute of normal time.

City -- making their first appearance at this stage of the competition after going out twice in the group stage -- will travel to Barcelona in three weeks time for the second leg with it all to do.