Third Eye Blind's Stephan Jenkins Met MGK at Emo Nite Before 'Semi-Charmed Life' Sample

Machine Gun Kelly and Stephan Jenkins met at an emo rock night in L.A. before the artist sampled his track ... which is a big deal, 'cause SJ has turned down others before.

We caught up with the Third Eye Blind frontman Wednesday and asked him about how he and MGK linked up ... 'cause Kelly recently sampled the song "Semi-Charmed Life" for his new track "Starman."

Stephan says he and Machine Gun Kelly met at an Emo Nite event last year -- a roving showcase where fans of the genre gather at different venues to hear DJs, or celebs like Jenkins, play some of their favorite songs in the emo genre.

Kelly introduced himself to Jenkins backstage, Stephan says ... and, the two built up a rapport.

Jenkins comments on MGK's genuinely sincere nature and the respect he has for all kinds of music ... and, he says he likes how MGK took 'Semi-Charmed' and used it to make something new and totally different from the OG track.

MGK must've really impressed Stephan over the last few months ... 'cause he finally signed off on Kelly using the song -- when he admits he's turned quite a few other artists down.

BTW ... Kelly's going around telling a story that seems straight out of a movie -- claiming he convinced a National Guardsman to let him into a Malibu neighborhood during the devastating L.A. wildfires earlier this year so he could get the sample cleared.

Jenkins confirms it's all true, adding Kelly pulled up in a pink Rolls-Royce ... but clarifies that MGK didn't come to his house, because he was staying with a friend at the time.