I left you last week with Mikhail Tal's knight dangling under attack on g4. What is going to happen to it? A humiliating retreat? Noooooo.
A great player like Tal would not have played 13...Ng4 without a good reply planned to 14.h3. So Tal - probably instantly - took on f2, sacrificing the knight!
Both players had seen this far. Gurgenidze thought that he has defended himself, and next 18.Nf3 would chase the black attackers back. But he missed one small detail...
All of Black's pieces are in the game, so he is ready for the final breakthrough. White's pieces are also all developed (and he even has one more of them!) but what a difference in strength! Every single black piece is doing more than its white counterpart. It's not surprising that Black can now crash through.
Black's 14...Nxf2 really allowed him to take control of the game! Pretty soon other players figured out that you better be careful when "The Magician From Riga" sacrifices a piece!