Our sources say … a week ago Thursday, after Katie filed, the hostility between the two was palpable and Suri became a weapon.  Katie wanted to strip Tom of all decision-making power in Suri’s life, and Tom responded by unleashing the biggest legal guns around to fight her.

We’re told what turned everything around was a series of conversations that Suri would be irreparably damaged by parental warfare.  It registered big time with both Tom and Katie, and it allowed their lawyers to strike a deal in what could be record time for this type of divorce.

Fact is … it generally takes celebs in these high-profile divorces a lot longer to realize how bitterness affects small kids, so credit to both.