Arc Warden (Miracle's hero, top right) has an ultimate ability that creates a clone of his hero that can use all of the same spells and items. Another spell of his is "magnetic field" that blocks all attacks from anything standing outside of it, and it works on buildings. The ancient (must be killed to win the game) was literally one hit from dying, but Miracle kept it alive by using magnetic field on it at the last second, and none of Alliance's heroes could get inside the bubble to hit it (storm tried to zip through it to get an attack off mid-air but he misstimed it and morphling could have waveformed to do the same but might have used his charges already. Either way, neither managed to pull it off in the panic of the moment). Once the first magnetic field expired, miracle used his clone to immediately put up a second one, keeping it alive even longer. Rinse, repeat, Alliance instantly buybacks, etc. until all of them are dead. Nigma then immediately yolos down mid and kills their ancient because Alliance's heroes won't respawn in time to defend their own base.

It was perfect repeated timing by Miracle controlling his hero and his clone that saved their ancient at the LAST second and kept it alive through multiple buybacks and repeated attempts by Alliance to finish off the building.