Lindsay Lohan has successfully paid off one of her enormous tax bills ... using Charlie Sheen's $100,000 check -- and TMZ has obtained official proof.

According to the official IRS document, Lindsay has paid her outstanding 2009 tax bill for $93,701 in full.

Sources close to Lindsay tell us, she used Charlie's generous check to cover the tab -- and has already applied the remaining $6,300 to her 2010 tax bill for $140,203 (only $133,000 to go!!!).

According to sources, Lindsay's still on the hook for her 2011 taxes too -- but she's actively trying to raise the money to get herself out of the red as soon as possible.