WOW Quest:The Valiant's Challenge (13726)  

A good strategy is to do the following:

• Stack 3 defends.
• Engage the champion
• Spam '1' until the champion moves to range.
• As soon as it is in range, use charge.
• Go a short way past the champion before beginning the turn.
• While turning around to re-engage the champion (with your mouse, keyboard is too slow - this is important) spam '2'. About 50% of the time you will get off a shield breaker and take off another of the champion's defends. If he does it to you, simply stack another defend back up to 3 and rinse/repeat until he submits.

This method is effective for all mounted combat.