Both sets of supporters have been criticised in the past for songs referencing the Munich and Hillsborough disasters but there was a more dignified air to proceedings at Anfield on Sunday following the publication of the independent report into the tragic events in 1989.
Sir Bobby Charlton handed flowers over to former Liverpool striker Ian Rush on the pitch while rival skippers Ryan Giggs and Steven Gerrard released 96 balloons in memory of those who lost their lives.
Sir Alex told MUTV: "Sir Bobby presenting the wreath to Ian Rush and both captains letting off balloons set the right tone.
"I'm pleased there was respect from each set of supporters. Hopefully, that's the crossroads now - a line in the sand.
"Nothing will stop the rivalry but it's gone beyond the pale in the past and hopefully that's gone now."