Opens a crucial diagonal against the white king, and this quickly translates into a mating attack.
1. e2e4  1... c7c5  2. g1f3  2... b8c6  3. b1c3 Anti-Sveshnikov. The author of the system considered the lines that avoid the Sveshnikov the only lines playable. 3... e7e5  4. f1c4  4... d7d6  5. d2d3  5... f8e7 Now it is almost an Italian but with a black pawn placed on the c5-square. This certainly weakens the d5-spot, but the question is, can White profit from that $2 6. a2a4  6... g8f6  7. c1g5  7... f6d7 Not a novelty, and certainly a move to know in this line. The knight can control the d5-square; therefore, Fedoseev preserves it. It is also generally desirable for Black to swap off his dark-squared bishop. 8. g5d2 That is the reason why Oparin keeps the dark-squared bishops alive. He did play this novelty though after a lengthy thought. 8... e8g8  9. c3d5  9... d7b6 This is why the knight is kept alive. 10. d5b6  10... a7b6 Black is getting ready for a kingside attack, and the move in the game does two things. It stabilizes the center and opens a file in case that White decides to hide his king there. 11. c2c3  11... g8h8  12. b2b4  12... d8e8 Thanks to the central stability, Fedoseev is ready to break open the kingside with f7-f5. His game seems far more straightforward and simpler. 13. b4b5 Oparin finds a clever plan to counteract. 13... c6d8  14. h2h4 That is White's point: he may also fight back for the kingside. 14... f7f5  15. h4h5  15... c8e6  16. d1b3 There is one serious issue that Oparin did not solve yet: where to hide his king. 16... e8d7  17. e1d1 An attempt to hide his majesty on the queenside, but this is a mistake. 17... f5e4  18. d3e4  18... e6c4  19. b3c4  19... d7g4 Double attack. 20. c4d3 And this makes things even worse. 20... c5c4  21. d3e3  21... d8e6 When the knight comes on the freshly created d3-outpost, the white king will have nowhere to hide. 22. h1g1  22... e6f4  23. d1c1  23... g4h5 Black won a pawn while building a huge positional advantage. The game is essentially over. 24. c1c2  24... h5g6  25. g2g3  25... f4d3  26. f3h4  26... g6e6  27. h4f5 The only active try, but