Theory of the delayed Jerome Gambit (1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.Bxf7+) has developed slowly. For example, transitions from the Semi-Italian opening (3.Bc4 h6) to the Jerome have been evaluated generally – e.g. White's "waiting" fourth move (4.0-0, 4.Nc3 or 4.d3) will be more useful than Black's 3...h6.
Occasionally a game pops up that illustrates more concretely the impact of waiting a move.
UNPREDICTABLE - badreligionnn
blitz FICS, 20101.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.d3
4...h6 5.Bxf7+
5...Kxf7 6.Nxe5+ Nxe5 7.Qh5+ Ke6
Previously, White has not been very successful in this line, scoring 27% in 15 games.
8.Qf5+ Kd6 9.f4
UNPREDICTABLE has lost two struggles with different 9th moves: 9.Bf4 Qf6 10.Qxf6+ Nxf6 11.c3 Ke7 12.Bxe5 d6 13.Bxf6+ gxf6 14.d4 Bb6 15.Nd2 Rg8 16.0-0 Be6 17.g3 Rg6 18.f4 Rgg8 19.f5 Bd7 20.b3 c5 21.d5 Bb5 22.c4 Bd7 23.Nf3 Kd8 24.Nh4 Kc7 25.Ng6 Rae8 26.Rfe1 Ba5 27.Re2 Bc3 28.Rc1 Bd4+ 29.Kg2 a5 30.Kf3 a4 31.h4 axb3 32.axb3 Rb8 33.h5 b5 34.Rd2 bxc4 35.bxc4 Rb3+ 36.Kf4 Be5+ 37.Kg4 Rxg3+ 38.Kh4 Re3 39.Nxe5 fxe5 40.Rcc2 Rxe4+ 41.Kh3 Bxf5+ 42.Kh2 Rgg4 43.Rf2 Rh4+ 44.Kg1 Re1+ 45.Kg2 Bxc2 46.Rxc2 Rxh5 47.Kf2 Rf5+ 48.Kxe1 h5 49.Kd2 Rf4 50.Kc3 h4 51.Rh2 Rf3+ 52.Kc2 h3 53.Kc1 Rg3 54.Kd1 Rg1+ 55.Kd2 Rg3 56.Kd1 Rg1+ 57.Kd2 Rg2+ 58.Ke3 Rxh2 59.Kf3 Rc2 60.Kg4 h2 61.Kf5 h1Q 62.Ke6 Qh6+ 63.Ke7 Ra2 64.Kf7 Ra8 65.Ke7 Qg7+ 66.Ke6 Re8+ 67.Kf5 Rf8+ White resigned, UNPREDICTABLE - bigchip, FICS, 2009; and
9.c3 Qf6 10.Qxf6+ gxf6 11.d4 Nd3+ 12.Kd2 Nxf2 13.Rf1 Nxe4+ 14.Kd3 Kd5 15.dxc5 Nxc5+ 16.Kc2 d6 17.a4 Bd7 18.b3 Re8 19.c4+ Ke6 20.Re1+ Kf7 21.Rxe8 Bxe8 22.Nc3 Bc6 23.g3 Ne7 24.Be3 Be4+ 25.Nxe4 Nxe4 26.Kd3 f5 27.Rf1 Kf6 28.g4 Ke6 29.Re1 Nf6 30.Bxh6+ Kd7 31.g5 Ng4 32.Bg7 Rxh2 33.Bf6 Ng8 34.Kc3 N4xf6 35.gxf6 Nxf6 36.a5 a6 37.Kb4 Kc8 38.Re6 Ne4 39.Rg6 Rh5 40.Rg8+ Kd7 41.Rg7+ Kc6 42.Rg6 Nc5 43.Ka3 Rh3 44.Rf6 Rxb3+ 45.Ka2 Rc3 46.Rxf5 Rxc4 47.Kb2 Ra4 48.Kc3 Rxa5 49.Kb4 Rb5+ 50.Kc3 a5 51.Rf6 a4 52.Rf1 b6 53.Ra1 Ne4+ 54.Kd3 d5 55.Rxa4 Kc5 56.Ra1 c6 57.Rc1+ Kd6 58.Kd4 Rc5 59.Rh1 Rc4+ 60.Ke3 Kc5 61.Rh6 b5 62.Ke2 b4 63.Ke3 b3 64.Ke2 b2 65.Rh1 Kb4 66.Kf3 c5 67.Rb1 Kb3 68.Kf4 Rc3 69.Rh1 c4 70.Ke5 Ka2 71.Kxd5 b1Q 72.Rxb1 Kxb1 73.Kxe4 Rc1 74.Kd4 c3 75.Kc4 c2 76.Kd4 Re1 White resigned, UNPREDICTABLE - fdy, FICS, 2009.
The text is sharper, even if it allows Black to play along the lines of one of the more spectacular refutations in the regular Jerome Gambit.
9...Qh4+
Destination: complications.
10.g3 Nf3+
Black continues along classical Jerome Gambit lines, unaware of the difference that d2-d3 has made in White's game. To maintain his advantage, he needed to retreat his Queen, not advance his Knight: 10...Qe7.
Another change in Black's options is that he does not have the thematic ...Qf6 at his disposal, since 10...Qf6 11.fxe5+ cannot be met by 11...Qxe5 because of 12.Bf4, winning the Queen.
After 10 Qe7 11.fxe5+ Kc6 12.Qg6+ d6 13.Bf4 Be6 Black would have been better.
11.Kd1
The key game from the Jerome Gambit line, abhailey -peonconorejas, net-chess.com, 2008 (0-1, 20) went 1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.Bxf7+ Kxf7 5.Nxe5+ Nxe5 6.Qh5+ Ke6 7.Qf5+ Kd6 8.f4 Qh4+ 9.g3 Nf3+ 10.Kd1 Ne7
analysis diagram
11.e5+ Kc6 12.Qe4+ d5 13.exd6+ Nd5
analysis diagram
14.gxh4 Bg4 15.Qa4+ b5 when Black's 4 pieces and the threatened discovered check added up to a quick win.
In the current game, the same strategem would flounder: 11...Ne7 12.e5+ Kc6 13.Qe4+ d5 14.exd6+ Nd5 15.gxh4 Bg4
analysis diagram
because White now has 16.h3, when Black's discovered check allows him to win the Queen, but the recapture by White's pawn on d3 gives him the better game
analysis diagram
If Black instead retreats his Bishop, White gets an even game after 16.h3 Bh5 17.c4 Ng5+ 18.Kc2 Nxe4 19.cxd5+ Kxd5 20.dxe4+ Kxd6 21.Nc3 Rhe8
Whew! Now, where were we...?
11...Qe7 12.Qd5 checkmate
Ouch.
As is often the case with the Jerome Gambit, the annotations are about subtlety while the moves themselves are lummoxes