Brooke Mueller -- I've Already Won the War ... Charlie Sheen Will Pay Out His Ass

Brooke Mueller is quietly smiling to herself -- because she believes she's already won her custody battle against Charlie Sheen ... all thanks to his self-sabotaging rants ... and it's gonna cost him big.

Sources close to Brooke tell TMZ, they believe Brooke has gained the upper hand in the custody war after Charlie's foul-mouthed blustering against Brooke, the judge, and the L.A. County Department of Children and Family Services.

Thanks to the diatribes, we're told DCFS now believes Charlie is off his rocker ... and it's more inclined than ever to give Brooke full custody of twins Bob and Max, which is what DCFS always wanted.

But that's not it -- we're told Brooke isn't just confident she'll get full custody, she believes the judge will now award her even MORE child support from Charlie than she previously received ($55,000 per month).

Ca-ching!