I am running power to an outbuilding 130' from main panel.Just need lights and a couple recepticals,planning on running 10-2. I have a outdoor rec. right above main panel which is about 3' of 12-2 and is the only thing on that circuit.Can I tie in to that rec. to keep from boring new holes through house? My concern was going from 12-2 to 10-2.Thanks for any help.

No way I'd use even that dedicated existing receptacle. Especially if the panel is right there.

You're going through all this trouble, run 10/3 and make it a multi-wire (shared neutral) circuit on a 20A two pole breaker.

I am planning on running 10-2 and a single circuit not 10-3

I am sorry I misread your post stanfortyman,I reread it and understand what you are saying,but I have enough 10-2 left over from another project.Thanks for your help.

If you have it that's fine. It's just a multi-wire circuit will help give you more power and also help with voltage drop.
130' is not all that far so the #10 should be fine at 120v for the loads you'll have.

I'd still run it right to the panel though.