The Dragon and the Apprentice (Book One of the Chronicles of Sir John the Worm)
by Sully Tarnish
A dragon and a wizard meet every ten years for a duel to prove who is the stronger. The duel always ends in a draw. Finally, realizing they are growing too old to continue fighting one another, the dragon and the wizard enter into a wager. They will each pick and train an apprentice. In ten years' time, the apprentices will meet and duel in their masters' stead.