Ok first you'll need to go out and buy a nice wand and staff, and make sure you get plenty of enchanting mats so that you're armour is higher than him (Even though he's level 14 and you're level 13).
When you get there, hide in the bushes and wait for him, hopefully nobody else had to fight him that day otherwise you might have to wait for him to regen and that'd suck balls.
Anyway hopefully he is there, and if he is, don't get to close or you might agro him, and that would forfeit your casting time. So while in the bushes, cast a shadow bolt from far away and after casting but while it's still in the air, hit him with all your DOTs, like corruption and curse of agony. At this time he'll be running towards you so start casting fear and hopefully by the time he gets to you it will have just finished casting.
While he's running away just snag him with your wand over and over or use shadow bolt, either way is fine. Just keep fearing him until he dies, remembering to DOT him with your curses when they run out.
If you win, don't forget to loot him, as I'm sure he'll have some sweat goods and shit, as level 14 wankers usually do.