Heat oven to 350°F (325°F for dark or nonstick pan). Spray bottom and sides of 15x10x1-inch pan with baking spray with flour.
In large bowl, beat cake mix, sour cream, water, cocoa, butter and eggs with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Pour into pan.
Bake 18 to 22 minutes or until toothpick inserted in center comes out clean. Cool about 45 minutes.
Spoon frosting into small microwavable bowl. Microwave uncovered on High 20 to 30 seconds, stirring once, until pourable. Spread frosting over cake; sprinkle with pecans.