Lindsay Lohan -- Her Ass Was a F****** Champion on 'Eastbound'

Lindsay Lohan knocked it out of the park on "Eastbound & Down" -- sources tell TMZ, she crushed her cameo Kenny Powers-style ... and even got a standing ovation from the cast and crew.

Sources close to production tell us, Lindsay didn't just conduct herself professionally while on set this week in North Carolina -- showing up on time and memorizing her lines backwards and forwards -- she was actually funny too.

As we reported, Lindsay is set to appear in the series finale, playing Kenny's illegitimate daughter.

After filming, we're told the cast and crew were so impressed by Lindsay's performance, they gave her a standing o. We're told the HBO show's co-creator Jody Hill hugged it out with Linds and thanked her for taking the gig.

Post-rehab fun fact: we're told Lindsay had a sober living coach with her the entire time she was on set.