In the starting position, only 2 types of piece can move: the Pawns and the Knights. All of the other pieces are trapped behind the Pawns. So it is common in the opening to move the Pawns in order to release the trapped pieces. The pieces are not considered "developed" until they move off the back rank, and this is one of the goals in the opening phase of the game: develop your pieces! An undeveloped piece usually cannot take part in the game.
Another goal in the opening is to influence or "grab control" of the center (the squares d5, d5, e4, and e5).
In this position each Pawn and each Knight can make 2 possible moves. Of these 20 possible moves, however, only 4 are generally played, and the most common opening move is the one that was played in this game...
1. e4
This moves the pawn to the center where it controls f5 and the central square d5, as well as occupying the central square e4. It also opens the diagonal f1-a6 for the light-squared Bishop, and opens the d1-h5 diagonal for the Queen. If Black does nothing to prevent it, White’s next move will be to move the Pawn at d2 to d4. Then White would control the squares from c5 to f5, severely cramping Black.
1… e5
Black imitates White’s move for all of the same reasons. This move also makes White think twice about moving the d2 pawn to d4, because now Black’s Pawn on e5 could take it.
2. Nf3
White develops the Knight towards the center, so that it controls the central squares d4 and e5. It also attacks Black’s undefended Pawn at e5. It’s usually a good thing whenever you can develop one of your pieces and attack one of your partner’s pieces at the same time!
If Black doesn’t do something to protect the Pawn on e5, White’s Knight will capture it next move.
2…Nc6
Black develops the Knight towards the center, controlling two central squares, and defending the Pawn on e5. Now, if White were to take the Pawn on e5, Black would reply by capturing White’s Knight with her own Knight. Since a Knight is worth more than a Pawn, White would be foolish to take the Pawn now.
3. Bc4
White puts his light-squared Bishop to work on the valuable diagonal a2-g8. This adds another piece to control one of the central squares, and it attacks the Pawn at f7: the weakest spot on the board in the early stages of the game (as it is only protected by the King.) With this move White has also cleared the way for Kingside castling.
3….Bc5
Once again, Black makes a similar move for the same reasons.
4. c3
White advances this pawn in order to support a move of the d2 pawn to d4 next move. If Black were then to capture the d4 Pawn with the e5 Pawn, White would recapture with this c3 Pawn and would end up with two powerfully placed Pawns in the center (at d4 and d5).
However, the move c3 has some drawbacks: In the opening, pieces, not pawns should usually be moved whenever possible (after the Pawns clear the way for them to come out), and the c3 square is usually the best square for the b1 Knight. With this pawn on c3, the Knight does not have a good square to move out to, as a3 is far from the center and the Knight is really only half a Knight on the edge of the board (influencing only 4 squares as opposed to 8).
4…Qe7
We normally don’t move the Queen this early in the game, because the Queen is too easy to attack out in the open in the early phases of the game, and her owner must waste time defending her rather than developing more pieces.
But White’s last move justifies Black’s Queen move. White now will lose a Pawn if he proceeds with his plan and plays the d2 Pawn to d4, because after Black’s e5 pawn captures the d4 Pawn, and White recaptures the Pawn on d4, Black will capture the undefended Pawn on e4 with her Queen, giving check. White will have to get out of check, which will give Black time to move the Bishop, and will result in Black being a Pawn to the good.
Let’s look at this variation move by move before we continue with the actual game…
White plays the d2 Pawn to d4...
Black captures the Pawn with her Pawn...
White recaptures the Pawn with his Pawn, attacking the Bishop...
But now the Black Queen captures the e4 Pawn with check, and after White defends against the check, Black will move the Bishop to safety (probably to b6) and Black will be a Pawn to the good.
Now let’s get back to the game and see what White really played.
This was the position after Black’s 4th move (moving the Queen to e7). Due to what we just saw, White wisely decides not to move the d2 Pawn to d4, and instead, he castles...
5. O-O
White castles the King to safety. Now White can once again move the d2 Pawn to d4. If, after exchanging Pawns, Black captures the e4 Pawn with her Queen, White moves the Rook to e1, pinning the Queen against the King, and winning Black’s Queen!
This should give you some idea of how valuable the castling move can be!
5…d6
This Pawn move gives additional support to the Bishop on c5 and the Pawn on e5. It also opens up the c8-h3 diagonal for Black’s light-squared Bishop.
6. d4
At last White moves the d Pawn up the board, hoping that Black will capture it with his Pawn, leaving White with the two central Pawns, and opening up the c3 square for White’s Knight.
6…Bb6
But, instead of capturing the Pawn, Black simply moves the Bishop to safety, leaving it to still bear down on the center.
Although White’s Pawns in the center appear formidable, the White position is shaky. The Pawn on d4 is attacked three times, and White must keep three pieces tied to its defense. Right now, White cannot move the Queen off the d file, and cannot move a Knight to d2 (as that would cut off the Queen’s defense of the d4 Pawn). Black also threatens to move her Bishop to g4, pinning the Knight on f3, and thereby taking away its protection of the d4 Pawn.
7. a4
White is threatening to move this pawn to a5 on the next move, and attack the Bishop. If the Bishop were then to take the Pawn, White would move the d4 Pawn to d5, attacking the only defender of the Bishop. If the Knight then moved, White would capture the Bishop with the Rook at a1 winning a piece.
Or, if after White’s Pawn moved to a5, Black’s Knight were to capture it, then Black’s Rook would take the Knight, and after Black’s Bishop captured the Rook, the White Queen would move to a4 with check, and would capture the Bishop on the next move. In this case White would win two pieces for a Rook and a Pawn.
Were you able to visualize all that? Let’s look at these moves on the board.
White moves the pawn to a5...
The Bishop captures the Pawn...
White moves his Pawn to d5, attacking the Knight, which is the only defender of the Bishop on a5. Now Black must move the Knight or lose it. If she moves the Knight, then the White Rook moves up from a1 and swallows up the Bishop.
But let’s go back a few moves and look at Black’s other possibility...
White has just moved the pawn to a5, and instead of capturing it with the Bishop...
Black decides to capture with the Knight. In this case, White would take his Rook...
and capture the Knight.
Not wanting to remain down a piece, Black recaptures the Rook...
With her Bishop. But now White creates a fork with his Queen...
White moves the Queen to a4, forking the Bishop on a5 and the King on e8. Black must get out of check, and after she does so, White will capture the Bishop.
A series of moves like this, resulting in some gain, is called a combination. But you should not embark on a combination such as this prior to developing all your pieces. White’s violation of this principle will catch up with him before too long.
Let’s go back to what actually happened in the game...
White had just moved the Pawn to a4, threatening to move it to a5, with all of the complications we just saw after Black captures it. Now it’s Black’s move, and she moves...
7…a6
Black moves this pawn to prepare a retreat for the Bishop. Now, if White’s pawn moves to a5, the Black Bishop can go to a7 , avoiding all the trouble that would come with capturing the Pawn. This also allows the Bishop to retain its hold on the a7-g1 diagonal.
8. a5
White still hopes that Black will take this Pawn.
8…Ba7
But Black does not fall for the trap; she retreats the Bishop as planned.
9. h3
White makes this move to prevent Black’s light-squared Bishop from coming down to g4 and pinning the White Knight on f3. But this move weakens the protective cover of the White King, something you never want to do willingly without a very good reason.
9…Nf6
Black develops the Knight towards the center, and with an attack on White’s e4 Pawn. Remember that developing with a threat is always good because your partner must make a move in defense rather than the move he or she may have wanted to make.
10. dxe
White exchanges Pawns, and opens up lines for his pieces. Unfortunately, open lines favor the side that is more developed, and in this case that’s Black.
10…Nxe5
Black recaptures with the Knight. This is much stronger than recapturing with the Pawn, because the Knight is now beautifully centralized and radiates its influence in every direction (something a Pawn cannot do). The disappearance of White’s Pawn on d4 has opened up the a7-g1 diagonal for Black’s dark-squared Bishop and it now takes aim at the f2 Pawn… and the King behind it!
Notice that White’s move has done nothing to relieve the threat on his e4 Pawn; the Knight at f6 still attacks it and nothing defends it.
11. Nxe5
White decides to exchange Knights, getting rid of Black’s powerfully placed Knight on e5. But in so doing, White’s Kingside Knight, the best defender of the castled King, also comes off the board!
11…Qxe5
Black recaptures with the Queen. Notice that White’s Knight has disappeared completely from the board, but Black’s Knight has been replaced, as it were, by the Black Queen, which now dominates the center and takes aim right at the weakened squares (g3 and h2) around the White King! Now Black has 2 pieces attacking the Pawn on e4, and it has no defenders!
12. Nd2
White defends the pawn on e4 by the Knight. Now White hopes that Black will take the Pawn, because White would then capture the Knight, and after the Queen recaptured White’s Knight, White would move the Rook to e1 and pin the Queen to the King, winning the Queen.
But Black is not interested in this Pawn.
12 …Bxh3!
Black sacrifices the Bishop for the h pawn. This is the Pawn which innocently moved here to prevent a pin. Black removes the offending pawn: a fit punishment for the crime of weakening the position and betraying his King!
But can Black afford to lose 2 material points? The answer in this case is Yes, because thanks to her developing them, her pieces are poised to take advantage of the ripped open cover around the King.
13. gxh3
White must take the Bishop, or be a Pawn down with nothing to show for it.
13…Qg3+
The Queen makes a crashing entrance! Notice how Black exploited the 2 main consequences of the Pawn’s move to h3: she captured the Rook’s Pawn itself, and then she used the g3 square (which was weakened by the Pawn’s advance) as a point of invasion.
White cannot capture the Queen with his f2 Pawn because it is pinned by the Bishop on a7.
14. Kh1
White makes the only legal move: moving his King out of check.
14…Qxh3+
Black destroys another defending Pawn, further exposing the King.
15. Kg1
Again, White’s move is forced as it is the only legal one. Note that Black now has gained 2 Pawns for her Bishop, but she also has gained a devastating attack!
15…Ng4
Black threatens mate next move (by moving the Queen to h2, which would now be supported by the Knight on g4).
White must either defend the h2 square, or give his King room to run by moving the Rook from f1 to e1 (but this would lead to immediate checkmate from the Bishop on a7 taking the Pawn on f2). So, White plays...
16. Nf3
The Knight now guards the h2 square and prevents immediate mate.
Black now reasons as follows: I have captured 2 of the Pawns around the King. If I can capture the third Pawn I will deprive the King of its last shred of protection. Currently the f2 Pawn is attacked twice: by my Bishop on a7 and my Knight on g4. But it is also protected twice: by White’s Rook on f1 and his King on g1. I need to drive off one of these defenders, or attack the Pawn a third time. Maybe I can do both...
16…Qg3+
Once again exploiting the fact that the f2 Pawn is pinned, Black attacks it a third time, with the Queen. White, once again, only has one legal move in reply...
17. Kh1
This move leaves the f2 Pawn with one less defender. It is now attacked 3 times and defended once. It is ripe for the plucking!
17…Bxf2
Black takes the Pawn with the Bishop, and White resigned. But, if White had played on, here is what probably would’ve happened...
18. Rxf2
White takes the Bishop, because any other move would let Black move his Queen to the h file, and mate would soon follow.
18…Nxf2#
But mate follows this move as well: the Knight captures the Rook and the King is mated: the Queen covers all the escape squares, and the Knight delivers the mate.