Shaun Alexander -- The Secret to NFL Domination ... Marriage!!! (VIDEO)

You can't spell dominate with 3 important letters -- I DO -- and it's no coincidence according to NFL legend Shaun Alexander ... who says his stats EXPLODED right after he got married.

The Seattle Seahawks great was out in Chi-Town for the Draft -- when we asked if marriage actually has an impact on NFL performance (you know, with Russell Wilson about to tie the knot).

The good news for Seattle ... Alexander says holy matrimony turned him into a virtual SUPER SAIYAN -- 'cause right after he got married in 2002, he became one of the BEST players in pro football.

Numbers don't lie.