Brian Robinson is speaking out for the first time since he was horrifyingly shot in D.C. on Sunday -- saying on Monday he underwent surgery for his injuries ... and, thankfully, it all "went well."

The Washington Commanders tailback, who was hit by bullets in what appeared to be a robbery attempt less than 24 hours ago, posted the positive message on his social media page.

In the note, he said he was thankful for everyone's prayers ... and added, "God is great!"