Place potato in a saucepan, and cover with water; bring to a boil. Reduce heat, and simmer 15 minutes or until tender; drain and cool. Shred potato.
Press zucchini on several layers of paper towels; cover with additional paper towels. Let stand 5 minutes, pressing down occasionally.
Lightly spoon flour into a dry measuring cup, and level with a knife. Combine the flour and next 6 ingredients (flour through pepper) in a large bowl. Combine milk and next 4 ingredients (milk through eggs); add to flour mixture, stirring until smooth. Fold in potato, zucchini, and onions.
Spoon about 1/4 cup batter onto a hot nonstick griddle or large nonstick skillet. Turn the pancakes when the tops are covered with bubbles and the edges look cooked. Top pancakes with sour cream and chives.