i dont think they blew it.. they were outplayed until the last 1/3 of the game when they were up a man. those offsides wouldnt have even been chances if they hadnt stepped offsides
But offsides kills momemtum and an attack, they are like turnovers.
And had it not been for that mone miraculous save by Keller, the US would have come up empty, despite the great effort.