SUNDAY AM: It was a bloodbath at the U.S. box office this weekend. Warner Bros. told me this morning its 'R'-rated 300 about the epic Battle of Thermopylae shattered the record for the biggest March opening ever, and scored the 3rd biggest 'R'-rated movie debut ever, with its $70+ million. (Or, $70.025 mil to be exact, though the studio didn't provide a breakdown.) Other studios say this 'Gladiator Gore-Fest' raked in $27.7 mil to $28 mil Friday and $24.3 mil to $24.8 mil Saturday and an estimated $16 mil to $17.2 mil Sunday from its 3,103 theaters. Toldja so... I said back on Tuesday that 300 was tracking huge -- even though most of its target audience fell asleep during that history lesson in school.