How to understand black's advantage in this line of the Polerio defense?

Question

In the following line of the Polerio defense, black has an advantage close to -2 according to the engine:

[FEN ""]  
1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. Ng5 d5 5. exd5 Na5 6. Bb3 Nxb3 7. axb3 h6 8. Nf3 e4 9. Qe2 Be7 10. Ne5 O-O 11. d4 exd3 12. Qxd3 Qxd5 13. Qxd5 Nxd5 14. O-O

I tried it out against an engine but kept making moves that equalised, because I really don't understand what black has here, or what I should be playing for with the black pieces. Obviously I see that I have better development and a maybe slightly better pawn structure, but I don't see how that translates into a coherent plan where black has the better chances.

Is the idea here simply that black has the bishop pair and a slightly better pawn structure and therefore should win the endgame after enough trades?

Answer 1

So in the final position, black actually has a really strong knight on d5, and if white tries to kick it away with c4, your just making your b3 pawn extremely weak, so black can target it, and pick up both the c4 and b3 pawns after moving your knight tob6 and then formulating a plan to attack the pawns with bf5.

[FEN ""]  
1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. Ng5 d5 5. exd5 Na5 6. Bb3 Nxb3 7. axb3 h6 8. Nf3 e4 9. Qe2 Be7 10. Ne5 O-O 11. d4 exd3 12. Qxd3 Qxd5 13. Qxd5 Nxd5 14. O-O Bd6 15. Nf3 Bf5 16. Na3 Bxa3 17. bxa3 Bxc2

The above is just an example of what might happen, but they are not the strongest moves, as you can see black tried to exploit the doubled b pawn with his light-squared bishop, which can be tricky to defend against

And yes yes, white has a knight on e5, but black can kick it away with bd6, if white tries f4, your just asking for trouble. Black has a bishop pair and you have just opened up your king to both diagonals.

Plus in this position, black has gained a tempo, right now white just castled, so black can develop with f5 to pressure the pawn with a tempo, or attack the knight. Then black basically has a few extra moves to play with

Answer 2

Black certainly has advantages. As you say, two Bishops, slightly better Pawns and a lead in development. But the position will not win itself and it would be very easy to give the advantage away. For example 14...Bd6? lets White off the hook after 15.Nc4. Just attacking a piece does not always win a tempo.

I would be inclined to play 14...Bf6 and if 15.Nf3 then 15...Bg4 16.Nbd2 Re8. There is no need to always to play forcing moves. Find moves that improve your position and don't let White improve theirs. Just develop to good squares and ask White to find a move.