Is it just to play an uncommon move to try and lure me into making opening errors? Also Stockfish says I blundered on move 18 but I was going for clearing the pieces off the board to win an endgame with an extra pawn, then I won more pawns, white blundered his queen and rage quit (left without resigning)
Anyway. Thoughts? Comments? And an answer to the first question would be cool. Thanks in advance.
-Autumn.
(1) The move 1.e3 in itself is not bad, as it transposes into interesting lines soon enough. It gives Black a lot of choice, which is in principle a bad idea (because White has to know a lot of very different opening structures to have a chance in the middlegame), but it can become a good idea if Black is swamped by the amount of choice or wastes time finding an opening scheme he likes.
With 1.e3 e5, White can for example play 2.d4 with a likely transposition into an exchange French after 2...exd4 3.exd4 d5. White can also play 2.c4 and an English opening (reversed Paulsen Sicilian if Black plays d5). The move 2.c3 indicates the intention to transpose to a Colle System (d4-e3-c3), but it's a bad move order because Black can push e4 as in the game. The game continuation can be considered as a refutation of 2.c3 after 1...e5.
Of course Black can play many other things than 1...e5 (probably the move White expects to face frequently after 1.e3). White can end up playing perfectly respectable openings like the Meran Semi-Slav (1.e3 d5 2.d4 Nf6 3.c4 e6 4.Nf3 c6 5.Nc3) or very offbeat schemes (1.e3 d5 2.f4 Nc6, a poor sideline in the Bird opening). He will need to rely on a very broad chess culture (a consequence of leaving a wide choice to Black) or to play refuted, non-instructive lines. By the way 2.c3 is always a mistake no matter what was Black's first move ("within reason" :D), because Black can play 2...e5 3.d4 e4 and White's c3 push is a wasted tempo.
(2) Your 18th move gives back the extra pawn in a few moves (on f7 and/or g7), leaving you with a clear positional advantage (-1 according to Stockfish) but it's far from the crushing advantage you could have if you had played 18...f6 or 18...f5 (Stockfish also gives 18...Qc6 for some tactical reason beyond my understanding). 18...f5 (or f6) saves the extra pawn, neutralizes White's f-file pressure and continues your plan without the slightest counterplay on White's behalf (-3 according to Stockfish). "What's not to like ?" (Carlsen's favorite sentence when he commentates for chess24).
In addition to A-Cielbleu's reply: The knight on e4 locks in the white bishop, and in turn the rook on a1. The bishop needs to stay on the c1-h6 diagonal to cover the entry point on d2 for the black rooks. On move 18 white is playing with 2 pieces down.
18. ... Qc6 looks very dangerous with threat of Rg5, which activates all pieces for a king-side attack. Can white hold? I don't know, but depending on white's time left on the clock, I'd play that move.
White's plan seems to play chess without opening theory.
I do not agree that 2 c3 is refuted by ...e4. For example in 1 e4 c6 2 d4 d5 3 e5 c5 also loses a tempo for black, where black tries to show that the push e5 weakens white's position. Carlsen even played 1 e4 Nf6 2 e5 Ng8 also playing on the weakening effect of the push e5.
5...dxc4 gives up your center. Your pawn at d5 is vital to protect your advanced pawn e4. You had to protect d5 with 5...c6.
7...Bg4 is bad. On 8 Qb3 both f7 and b7 are under attack. It is no good idea to force your opponent to play a good move. Fortunately for you he failed to notice.