How do I fix a small tear+long run in a capilene 2 baselayer?

The sleeve of my capilene 2 baselayer top has a small tear with a 3 in long run extending from it. I tried seeing if I could use a satin stitch with needle and thread to repair it , but found that trying to repair something on a sleeve as opposed to on the main body (where you have a lot of room to maneuver your hands) too difficult for a newbie. Any tips/recommendations