Oh no, not my Ed!!!!  British singer ED SHEERAN had his first night opening up for TAYLOR SWIFT on Wednesday night, and he made it memorable . . . by slipping and falling pretty hard onstage.

In the middle of a song, he was standing on a speaker, and was attempting to jump over to another one . . . but he misjudged it, lost his balance, and fell.

It sounds like he's fine.  He performed another show last night, and afterwards Tweeted, quote, "Eating a whole melon right now."

(--Here's video.  It happens at the 1:42 mark, at the very end of the clip.):