visayanbraindoctor: <CapablancaFan: 15...Nxd4! combonation was a little hard to see. It's actually an indirect attack on the bishop on f4!>
Yes the Bishop at f4 was unprotected. Its weakness is unexpectedly exposed by the discovered attack on the c5 Knight by Black's c8 Rook with 15... Nd4! And then upon 16. exd4 Bxc5, it turns out that the d4 pawn is pinned because of the unprotected white Bishop on f4.
But it's easy to overlook that, especially when one is attempting to initiate a series of tactics or combination with 15. Nc5. Suddenly Dus Chotimirsky's own combination falls apart. One had to be very careful in attempting combinations or a series of tactics against the young Capablanca. He saw every tactic hidden in a position, and if one's tactical series were unsound, Capa would rip it apart with his own tactics.
Seems to me that the peak Capablanca is the only chess player in history who had the ability to consistently see all the little 'petit' combinations and tactical shots hidden in complex positions. Since a common way to lose a chess game is to miss tactical shots, and Capa wasn't missing any, this made him nearly immune to making losing errors. This is the true secret of his invincibility.