I'd sand blast that little spot. It will be clean and even feathered out a bit. If you have a compressor but don't have any sandblast stuff, look on CL for a little cup (gravity feed) blaster.
Or this little guy for 15 bucks.
Abrasive Blast Gun with Bag
If you have an air nozzle, you can just about do that job with some fine sand in a jar and a small hole punched in the lid. Simply drop a column of sand into the air stream in front of the spot.