While in the final position, checkmate is still a move or 20 away, it's clear that White is lost. Black is a piece ahead with no compensation for White at all. People resign in such a position already on the higher level of club play. In a normal (i.e. non-blitz) game between grandmasters, White would probably already have resigned by move 30.

    [FEN ""]
    [White "A. Smirin"]
    [Black "V. Anand"]
    [Event "New York Intel Active (blitz)"]
    [Result "0-1"]
    [Date "1994"]
    [StartPly "100"]

    1. e4 e5 2. Nf3 Nf6 3. d4 Ne4 4. Ne5 d6 5. Nf3 d5 6. Bd3 Nc6 7. O-O Be7 8. c4 Nb4 9. Be2 Be6 10. Nc3 O-O 11. Be3 Bf5 12. Rc1 dxc4 13. Bc4 c6 14. Ne5 Nc3 15. bxc3 Nd5 16. Qb3 f6 17. Qb7 fxe5 18. Qc6 Be4 19. dxe5 Kh8 20. Bd4 Rc8 21. Qa6 Nf4 22. f3 Rc6 23. Qa4 Rc4 24. Qc4 Bd3 25. Qc6 Ne2 26. Kh1 Nd4 27. cxd4 Bf1 28. Rf1 Qd4 29. f4 Qe5 30. g3 Qc5 31. Qe4 Bf6 32. Kg2 Rc8 33. Rf2 Qc6 34. Qc6 Rc6 35. g4 h6 36. Kf3 Rc3 37. Ke4 Kh7 38. Re2 Rc4 39. Kf5 Rc5 40. Ke6 Rc4 41. Rf2 Kg6 42. h3 Rc3 43. Rh2 Rf3 44. f5 Kg5 45. a4 Kh4 46. Kd5 Ra3 47. Kc6 Ra4 48. Kb7 a5 49. Kb6 Ra3 50. Kb5 Rh3