Jerome Gambit: How Did That Happen?

Watching a good player who is skilled in playing the Jerome Gambit often inspires the question How did that happen?

Starting from a theoretically "lost" position for White at move 4, the following game moves forward until, 10 moves later, White has the attack and the advantage. Black has clearly missed some drawing lines, but still - How did that happen?

Wall, Bill - Guest2614882
PlayChess.com, 2017

1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.Bxf7+

4...Kxf7 5.Nxe5+ Nxe5 6.d4 Bxd4 7.Qxd4 d6 8.Nc3 c5 

A typical kind of position for Bill in his preferred 6.d4 variation. Sometimes the pawn move to kick the Queen helps, sometimes not.

9.Qd5+ Ke7

It is always interesting to see, in this kind of position, if the defender will choose development over material, and elect for 9...Be6, allowing 10.Qxb7+. This is not a terribly complex issue - Black can make the offer, and White risks sidelining his Queen if he accepts - but often the cost on seeing this through is time off Black's clock.

By the way, Bill has also faced 9...Kf6, which did not turn out well:  10.f4 Be6 11.fxe5+ Ke7 12.Qxb7+ Black resigned, Wall,B - NN, lichess.org, 2016.

10.Bg5+ Nf6 11.f4 Neg4 

What do we have here? Things are getting messy...

Stockfish 8 prefers 11...Nc6 and gives a line will all sorts of contortions - before ending in a draw by repetion.

For now, it's time for White to open attacking lines.

12.e5 h6 

A standard idea: counter an attack with an attack. However, here Black, possibly thinking that he is striving for advantage, misses an opportunity to keep the game level: 12...dxe5 13.fxe5 Qxd5 14.Nxd5+ Kd7 15.exf6 Re8+ 16.Kd2 Re5 17.f7!? Rxd5+ 18.Kc3 Rf5 19.Rhf1 Nf2 20.Bh4 Rxf7 21.Rxf2 Rxf2 22.Bxf2 with an even endgame.

13.exf6+ gxf6 14.Bh4 

There was no need to explore the further sacrifice 14.O-O!?, as the text is fine - although I will warn Readers not to reach this position in the future against Bill without exploring that move. 

14...Re8 15.O-O-O Kf8

Black has castled-by-hand, but his King remains at risk, especially with White's lead in development.

16.Qh5 Kg7 

The brave King defends his pawns - proving, again, how frustratingly backwards the Jerome Gambit can be sometimes for the defender. His best plan involved the alternative 16...Qd7, that is, a move that commits the classic error of blocking his light-squared Bishop, which in turn blocks his Queenside Rook...

17.Nd5 Be6 

18.f5 

Attacking the Bishop and un-protecting the Knight (which is protecting the Kingside).

Black is worried about the two minor pieces attacking his pawn at f6 and the subsequent possible fork of his King and Queen, so he figures it is time to eliminate the white Knight - alas, that will not work.

18...Bxd5 19.Qxg4+ Kh8 20.Qg6

Black resigned

White's Bishop will come to f6 with check, and either win the enemy Queen or force checkmate.