Wolves are killing for a living. In a way a dog fighting against a wolf is like a regular human fighting against a trained MMA fighter. 

Some dogs are no joke though, and the mind plays a big role. How bad does the dog want to win etc. Usually if a dog is defending something he will fight harder. Rotweiler has a bite force of over 300 pounds, coming close to the average bit force of a wolf which is around 400 pounds. Some dogs are a formidable opponent. 

This dog did a great job defending its owner, look at its face now,