Declining the Bishop sacrifice in the Jerome Gambit transforms the nature of the game. Instead of a tactical battle, there is a much quieter conflict, where the attacker has an extra pawn, but the defender has better development.
Clearly, White must reformulate his plans.
According to The Database, White scores 52% against 4...Kxf7, 62% against 4...Kf8, and 67% against 4...Ke7.
So, in the Jerome Gambit Declinded, White must resign himself to grinding out a win - but he realizes increased success over the Jerome Gambit proper.
(My own experience has been a bit different. Out of 456 games that started 1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.Bxf7+, my opponent declined the Bishop with 4...Kf8 only four times [I scored 75%] and with 4...Ke7 only three times [I scored 100%]. When I faced 4...Kxf7, I scored 82%.)
hamedkargarfard7 - JuanviPascual
Jerome Gambit Classic #1, Chess.com, 2024
1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.Bxf7+
4...Kf8
Declining the sacrifice.
Both players now show patience in developing their game and moving it forward.
5.Bb3 d6 6.d3 Nf6 7.Bg5 Nd4 8.Nbd2 h6 9. Be3 Bg4
I would guess that both players would be surprised to learn that Stockfish 16.1 (34 ply) evaluates White as being almost 2 2/3 pawns better. (I was.)
10.h3 Nxf3+ 11.Nxf3 Bxf3 12.Qxf3 Qe7 13.Bxc5 dxc5 14.O-O-O
White accumulates small advantages: the extra pawn, the minor exchange, the safer King, the better pawn structure.14...b5 15.Bd5
Now, and for the next few moves, 15.Qf5, infiltrating the Kingside, is an even better idea.
15...Rc8 16.g4 g5 17.Qf5
The Queen steps into a gap in Black's defense.17...Kg7 18.h4 c6
Hoping to eject the enemy Bishop, but events overtake this plan. More dynamic as 18...Nxd5 19.exd5 Rcf8.
19.hxg5 hxg5 20.Qxg5+ Black resigned
The second player's defense has collapsed, and checkmate is coming.
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