Hilary Duff Files for Divorce ... Mike's Wild Night Was Last Straw

Hilary Duff has finally pulled the trigger on her marriage, filing for divorce from hubby Mike Comrie ... and it looks like Mike's wild night in Bev Hills was the tipping point.

Sources close to the couple tell TMZ ... it's NOT a coincidence Duff filed her docs a day after the Daily Mail reported Mike was drunkenly propositioning women at Mastro's steakhouse in Bev Hills.

Hilary -- who hired attorney Laura Wasser -- cites the usual irreconcilable differences as the reason for divorce. She lists the date of separation as January 2013.

In the docs, Hilary asks for primary physical custody of their son, Luca, who turns 3 next month. She wants Mike to have visitation, but sources connected with the couple say she's concerned that his partying and drinking could adversely affect their kid.

The couple has a prenup, but neither spouse is struggling in the money department. Hilary wants her earnings and other stuff to remain her stuff.

Hilary and her NHL star husband were married in 2010 and when they split Hilary's mom, Susan, said, "They're better friends than a married couple."