The ayatollahs got into control because the Shah used them to overthrow the parliament (Behbahani and Falsafi and finally Kashani), used them to attack the left etc.  In fact, as I mentioned in another post, one of their first acts (1955) were the Shah and Falsafi conspiring to start an anti-Bahai campaign which caused riots which killed Bahai.<p>The US and shah and Savak did too well stamping out secularism, left-wing ideas, even liberal ideas about parliament, democracy etc.  Eventually the ayatollahs and Bazaari etc. amassed great power, and turned on the Shah.<p>Mossadegh was never in the pocket of the ayatollahs, but he did try to qualm moderates like Kashani.  But Kashani eventually turned on him (the hard-line preachers had far before).