Kelly Slater -- How I Pulled Off that Epic 540 [Video]

So, how the hell did surf god Kelly Slater pull off his insane 540 spin in Portugal last week???

The 42-year-old legend joined us on "TMZ Hollywood Sports" to explain ... telling us it wasn't just skill -- there was something in the air that day.

In case you haven't seen it by now, the trick has been the talk of the surf world ever since Slater pulled it off ... and for good reason -- it's super hard to do.

Check out the clip -- there has never been a bigger sports star who's still so humble about pulling off such a tremendous feat.