WASHINGTON - Rick Santorum is the winner of the Louisiana Republican presidential primary, defeating GOP front-runner Mitt Romney in yet another conservative Southern state.

Santorum is Romney's chief challenger and a former Pennsylvania senator who has won previous contests in Tennessee, Mississippi and Alabama.

The Louisiana victory was unlikely to change the overall dynamics of the race. Santorum still dramatically lags Romney -- the former Massachusetts governor -- in the hunt for delegate to the GOP's summertime nominating convention. Former House Speaker Newt Gingrich of Georgia was far behind in the Louisiana vote count.