All you have to do, is queue for a 5v5 skirmish, wait for the queue to pop, and typically you'll get in a match without anyone in it. Once the arena timer counts down 60 seconds to none, you'll snag the achivement (since in reality, you are the last man standing)
Obviously this is an exploit, because it gives you an advantage as to getting the achievement (one step closer to arena master). AND this is bugged because in the achievement text it says "A Ranked Arena Match".
Enjoy!
ps: alles geklaut
