My Most Shocking Blunder Ever

I THINK I must have been overdoing the chess of late, causing tiredness and staleness.
How else to explain the following shocker from this morning's eighth round of the Northumbria Challengers?

Black to make his 27th move in Michael Hubbard (1946/174) - Spanton (1881/168)

*****
*****
*****
*****
*****
Black wins easily after 27...Nxc5 28.Ba3 Kg8. But note that 28...Kf7? is much less clear as White has 29.Bxc5 Rxc5 30.Nb7 with Nd6+ to follow.
Instead the game saw 27....Rxc5?? 28.Nxb7 (1-0, 44 moves)