UFC middleweight champion Israel Adesanya paid a visit to the TMZ office on Thursday ... and naturally, we had to put his world-class skills to the test.

The Last Stylebender was up for the challenge ... saying he'd love to knock a cup off someone's head with a round kick -- and none other than our fearless leader, Harv, volunteered to get a front-row seat for the demo.

Worth noting -- Adesanya is the best of the best ... so we figured HL was never in any real danger. Harvey was not as convinced, which is obvious in the video.

The time came for Adesanya to show off his kick ... and thankfully, he knocked the cup off cleanly!!

The whole office cheered, while Harvey breathed a huge sigh of relief.

Now, a source -- whose name rhymes with Shmarvey -- swears Izzy's foot made contact with Harvey's head, but video doesn't support that at all. IF anything at all, HL felt the cup zooming off his head ... which just shows the kinda impact these kicks can make.