Opportunity Attack, Ready Action, & Eldritch Blast/Repelling Blast



Scenario:

A druid ally is in melee range of an enemy berserker and decides to move away, provoking an attack of opportunity from the berserker.

My character has readied an action: Cast Eldritch Blast (with Repelling Blast invocation) on the berserker in question if he attacks the druid.

What I think happens

The druid’s movement is interrupted by the attack of opportunity which is in turn interrupted by the readied Eldritch Blast. Assuming the Eldritch Blast hits, I can push the berserker out of melee range of the druid, thereby negating the attack of opportunity.

Is this correct?

Similar situations

What if, rather, the trigger was the druid moving? What if the trigger was the berserker raising his weapon or rearing back in preparation for an attack?