I cant believe someone asked this question?! And I cant believe I am posting to this stupid question! lol You are asking if a player who barely can play chess can win against a grandmaster? Gee! What do you think? Grandmaster would always win 1300 player in most cases playing without a queen! Could someone who just started boxing lessons beat Mike Tyson in his prime? lol
Well the question isn't, would you favor the 1300 to win, it's, could the 1300 win despite the odds against it.
Well, the FIDE elo rating system is done with that equation. i.e. if the FIDE elo system is well done, the expected result of a 10000 games match between a 1300 and a 2700 will be 3-9997
3 wins and 9997 losses. That is actually a very good chance.
It's reasonable to expect the formula to lose its predictive power in extreme cases like this. Actually that's already been shown for rating gaps as big as 500 (I forgot the threshold). Lower rated players consistently score a little better than predicted.
So that might suggest that the chances are even higher than 3 out of 10000, not lower :)