The Olympian just took gold in the men's 100m in a heart-stopping finish ... narrowly edging out Jamaica's Kishane Thompson by .005 seconds to win Olympic Gold.

In fact, the race was so close commentators initially thought Thompson won ... before the photo finish proved otherwise.

With Lyles' win, he takes home the gold and the unofficial title given to the winner of the Olympics 100m -- "World's Fastest Man" ... a big honor especially considering the X beef NL engaged in last year.

ICYMI ... Lyles won three golds at the World Athletic Games in Budapest last year -- and promptly called out NBA title winners for referring to themselves as world champions 'cause they only play other North American teams.

This prompted swift backlash from Drake, Kevin Durant, Draymond Green, Devin Booker and more stars who felt Noah was being downright disrespectful. Giannis Antetokounmpo later came out and backed Noah up ... but, fair to say he's persona non grata in NBA circles.

We caught up with Noah who told us he didn't give a single you know what about how NBA players were feeling ... adding they totally missed his point about wanting to give track the same level of exposure as basketball.