Keres-Tolush, Moscow 1957
The losing move is 13…Bxg5. The real beauty of this game is in the sidelines. Here is the best example, White is winning after 13..Qc5, 14.Nd5! exN, 15.Nf5, and if ..Nxe5 the e-file gets opened up against the Black king.
I figured out the end, if 29..Qe2, then 30.Qb4+ will mate (30..Ke7, 31. Rf7+ Ke8, 32.Qe7 mate), or 30..Ke5, 31.Qf4 mate) if 29..Qd2, then 30.Qf3 (…queen moves), 31.Qd5+ wins (..Ke7, 32.Nd8! followed by 33.Rf7+ Ke8 and White will mate regardless of anything Black just played, for example Qe6+ can be threatened, and then Qxe7 mate).