<Why? The kingside should not be weakened. 6...dxe5 7.dxe5 Nc6 is the natural and good continuation. White is better, but not severely.>

7.f4?

<Incorrect. The immediate 7.Nc3 develops and causes headache for Black.>

7...Nd7

<I think somewhat better is 7...dxe5 8.dxe5 Qb4+ 9.Qxb4 Bxb4+ 10.Bd2 Bxd2+ 11.Nxd2 fxe5 12.fxe5 Nc6>

8.Nc3 fxe5

<In Greco vs NN, 1620 and in P Damiano vs NN, 1497 Black took with the d-pawn.>

9.Nd5?!

<While still being better, the objectively most precise play was 9.fxe5! dxe5 10.Nd5 Nf6 11.Nxe7 Nxe4 12.Nxc8 Rxc8 13.Bd3 Nf6 14.dxe5 with a serious pull.>

9...Nf6 10.Nxf6+

<10.Nxe7 Nxe4 11.Nd5 Kd8 12.Bd3 and White is OK.>

10...gxf6 11.Bb5+

<Objectively better was 11.fxe5 dxe5 12.Be2 exd4 13.Qxd4 Bg7 (or 13...Qb4+ 14.Qxb4 Bxb4+ 15.c3) 14.Kf2 and White has the upper hand.>

11...c6 12.Bxc6+

<After 12.Be2?! either the d- or f-pawn should be pushed and Black is not worse.>

12...bxc6 13.Qxc6+

<13.0-0? d5 with a huge center.>

13...Kf7

<Or else 14.Qxa8 is good.>

14.Qxa8??

<Capturing a poisoned rook. 14.Qd5+!! Kg7 (now Rg8 is too slow) 15.Qxa8 exf4+ 16.Kf2 Bb7 17.Qxa7 Qe4 18.d5 Qxc2+ 19.Kg1 Qd1+ 20.Kf2 leads to a perpetual. But what if Black places the king on g6? 15.f5+!! Bxf5 (15...Kxf5?? 16.0-0+, and if 15...Qe6? or 15...Be6?, then White simply captures on a8 with way better prospects.) 16.Qxa8 exd4+ 17.Kf2 Be4 18.Qb8 d5 19.Re1 achieves a draw!>

14...Bb7

<Interestingly, the immediate 14...exd4! is stronger, as it forces 15.Kf2 Bb7 16.Re1 Bxa8 17.Rxe7+ Bxe7, and I don't see how can White survive. 15.Be3 is impossible (a little bit more about this laughable on move 16), as after capturing with the queen, Bg4 ideas will create a mating net.>

15.Qxa7 exd4+ 16.Kf2

<The computer likes the absurd 16.Be3!? Qxe3+ 17.Kd1 line. I guess I need to check it deeper, why is it favourable instead of 16.Kf2 - maybe the queenside pawns can generate some kind of counterplay. White is on the verge of losing in both variations, certainly.>

16...Rg8 17.Rg1 Qe4 18.g3

<In an already terrible position NN throws away the game at once. 18.Qa5 Rxg2+ 19.Rxg2 Qxg2+ 20.Ke1 Qg1+ 21.Ke2 Be7 22.Qh5+ Kg7 23.Kd3 Ba6+ 24.c4 Qf1+ is a nightmare for White, but at least there is some space for Kieseritzky to blunder away the attack.>

18...Qxc2+ 19.Kf1

<19.Ke1 does not save the game. After 19...Qe4+ Black's pieces will invade, anyway.>

19...Qd1+

<The digital monster announces a mate in 20. Not extremely surprising.>