Way too rushed at the moment, but I'd like to thank
Mithalwen for starting up this thread.
I will try & put something together on this tonight - there are numerous examples of these wizardly duels in the traditional literature - especially in Northern myth- as I mentioed in the Chapter-by-Chapter post that started this off, we find it in the Mabinogion, The Kalevala, The Eddas, & also in various Irish legends. Also, there are various 'magical ballads' depicting a conflict between, say, a young boy & the False Knight on the Road.
The 'Word of Command' is a more difficult concept - is it more than simply the 'topping phrase' in the duel - is it a qualitatively different power in the legends as it is in Middle earth? - I will have to look into this a bit more.
I suppose we can say that the Ainulindale represents this kind of wizardly duel on a cosmic scale - the Ainur loyal to Eru sing their 'spell' & those who side with Melkor sing theirs, but the 'Word of Command' is spoken by Eru - 'Ea!'.
On second thoughts, maybe this is not a subject that can be dealt with in a single post
