1. e4 c5 2. Bc4 Nc6 3. d3 White has activated his bishop before closing off the diagonal. White could also have delayed the d-pawn move trying for d4 to gain more space e.g. Nf3 with d4 to follow would be a main sicilian line
e6 Threatens d5 and supports c5. Blocks in blacks light square bishop ( black hopes temporarily )
4. Nc3 Develops and stops d5
Nf6 5. Bg5 Pins the knight. f4 was also interesting threatening to kick the knight back to g8 and really cramping up black
Be7 breaks the pin by developing the bishop to the only square that will make sense in the early game ( d6 would block blacks d-pawn and fianchettoing this bishop would weaken blacks pawns on the kingside with darksquare holes ( h6,f6,d6 ) )
6. h3 Seems to be a waste. g4 was already covered by the queen even if the knight planned to go there. Again f4 looks better here.
a6 black has little opportunity on the kingside. h6 doesn't make sense as the white bishop is no threat and could potentially be attacked with a discovered attack if anything moves within the black knights range. Qc7 or Qb6 was interesting but remove support for a d-pawn push
7. Nf3 threatens e5 and prepares castling
b5 kicks the bishop back. white cannot play e5 becuase e5 Bxc4 exf6 Bxf6 Bxf6 Qxf6 dxe4 leaves white with doubled pawns and black has a bishop to knight advantage which helps since the game is opened up and blacks queen is also active
8. Bb3 b4 Kick the knight off so that d5 can be played
9. Ne2 although the knight couldn't have been kicked off h4 Ne2 is more flexible
d5 10. exd5 This is not necessary. It gives black too much space. e5 gets interesting and Ng3 balances blacks queenside space with whites kingside potential
exd5 Nxd5 doesn't look as good because it leaves white with the queenside pawn majority, the night on d5 isn't well placed there and blacks dark bishop shouldn't be allowed to be traded ( since black has a space advantage he shouldn't trade down without cause )
11. O-O h6 I think Be6 or o-o was better here. h6 looks unneccessary in retrospect
12. Bxf6 Gives black the two bishop advantage unneccessarily
Bxf6 Incidentally attacks b2
13. Rb1 protects b2. d4 might work better here.
O-O 14. Nf4 Threatens d5
Be6 develop and protect
15. Nxe6 removes blacks two bishop advantage but strengthens blacks centre
fxe6 16. Re1 threatening the backwards e6 pawn and entering the half-open file
e5 Moves the pawn to a more supported square. This move is a mistake as Ba4 can undermine one of those defenders. Qd6 or Re8 are better
17. Ba4 Rc8 18. Nxe5 The wrong order. Bxc6 Rxc6 Nxe5 wins the pawn
Nxe5 White is down knight for pawn
19. Qh5 threatens to win knight and bishop for rook
Qd6 stops the exchange ( Qa5 and Bg5 fail )
20. Rbd1 Nxd3 This move is probably too impatient. The idea behind it is that it wrecks whites queenside pawns ( the knight is exchanged for two pawns, but the other two are no longer connected so should eventually fall. From this point of view it wins four pawns for a knight ) . It also guarantees a d4 post for the bishop.
21. Rxd3 Bxb2 22. Rxd5 Qf6 Creates a battery on the f-file. Note that Rxc5 loses a rook after Qxf2+
23. Rf1
Bd4 Positions the bishop on its outpost. It can't be knocked off. Incidentally pins the f2 pawn to the king. Kh1 expected blunting blacks immediate threats
24. Bb3 Threatening discovered check winning the queen
Kh8 Avoid discovered check. h8 is better than h7 can be attacked by whites queen and bishop
25. Qe2 "Protects" f2
Rce8 pushes the queen off the white square that she can protect f2 from
26. Qd2 Qh4 The queen still attacks f2 but this allows the rook to directly attack f2, so that it can go in ahead of the queen.
27. Qd1
Rxf2 This move was calculated throught the sequence that follows down to move 37. There is a sequence of checks that white can perform that black has only one response to, but these end with black winning an exchange. Bxf2 was not played here as it only wins a pawn and has no obviously useful continuation after the Kh1 response
28. Kh1 A discovered attack is threatened on the king winning the queen ( i.e. Rd2+ ) so either the rook must be taken or the king must move. Rxf2 fails to Bxf2+ where the king is forced to h1 either immediately or after Kh2 Qb3+ Kh1 when Re1+ forks the king and queen
Rxf1+ Not Qg3 Rxf2 Bxf2 Rd8 pinning the rook
29. Qxf1 Otherwise the queen is lost
Re1 pins the queen to the king but doesn't win it due to the following sequence
30. Rd8+ Whites queen is lost if white can't maintain check or threaten blacks queen
Kh7 Forced
31. Bg8+ Kg6 Forced as Kh8 merely repeats the position
32. Bf7+ This move is not immediately obvious. The white pinned queen supports the bishop. Rd3+ fails after Bf6
Kg5 Forced as Kh7 repeats the position
33. Rd5+ Be5 Not Re5 which releases whites queen for all sorts of mischief
34. Rxe5+ Rxe5 Finally releasing the pin on the queen, but wins the exchange
35. Qc1+ Forced. If the queen doesn't leave the first rank then Re1 wins the queen. If the queen leaves the first rank without check then Re1+ will be followed by Qf4+ and mate on the way. The white queen can't get from its current position to somewhere that blacks f4 except the text move
Kf6 Keeps the Re1+ threat of winning the queen and threatens to win the bishop
36. Qb2 Pinning the rook. Protects the bishop indirectly. The other move was Qf1+ Ke7 where the queen can't give check and must get off the back rank due to Re1+ threat. This would then lead to Qf3 Qf6 Bd5 Qxf3 Bxf3 where black is a rook and pawn vs bishop up in the endgame
Qe1+ Giving check and supporting the rook so the bishop is lost
37. Kh2 Kxf7 The end of the sequence calculated back 20 moves ago
38. Qb3+ White is now going to look for perpetual check by alternating the queen between the eigth rank and the h7-d6 diagonal. Getting the black king behind his two pawns and either blocking the black rank with the rook or blocking off the diagonal will achieve this e.g. king on h7 and queen and rook controlling the diagonal, or king on h8 and rook on the eith rank
Re6 39. Qf3+ Kg8 Following the plan
40. a4 Qe5+ Black wants to open up the white king so tries to position the queen where she covers the h2-b8 diagonal and getting the rook on the first rank. This would provoke g3.
41. Kh1 Qf6 The threat is Qe7 getting the queen behind the rook allowing Re1+ and Qe5+ opening up the white kings position
42. Qa8+ Unfortunately for white they do not control e4 to go with a8
Kh7 43. Qd5 Re1+ 44. Kh2 Qf4+ Qe5+ trades queens which is fine but slower
45. g3 Re2+ 46. Qg2 Rxg2+ 47. Kxg2 Qe4+ 48. Kf1 Qxc2 49. g4 b3 50. g5 b2 51. g6+ Kxg6 52. h4 b1=Q# 0-1