The positions arising from the Open Spanish contain ideas so different from the usual Ruy Lopez that I sometimes wonder whether it should really be considered part of it at all. It is an open game with unbalanced structures and sharp play but compared to the Sicilian, for instance, for which the previous description would also apply, there is an important difference; there is a certain degree of stability and solidity in the Open Spanish which distinguishes it from the sharper realms of the Sicilian and puts this line in its own unique category of opening ideas.
The popularity of this line increased significantly after the famous 1978 Karpov Korchnoi match where Korchnoi played it and demonstrated many interesting ideas. Still, the line never became fully mainstream until quite recently when I noticed an increased level of attention towards it. It is a practical line as it comes at a very early stage of the opening; White can’t avoid it once they have committed to the Ruy Lopez. That is quite a large advantage of the Open Variation compared to others. For example in the the Marshall Attack, another response to the Spanish about which I have previously written a book, White has numerous ways to avoid the line entirely and so there is a whole other branch of Anti-Marshall theory which Black must study too. Here this is not the case. While writing this book I also noticed that many lines are simply underrated from Black’s perspective for no clear reason. Black remains very solid and retains the possibility for counterchances. I am of the opinion that this line simply awaits more analysis and attention and will inevitably become more theoretically relevant in the future, perhaps after the catalyst of an elite player taking it up seriously, similar to Korchnoi in the past.
We can consider this as the starting position of the line. As we can see, Black is much more actively placed compared to other lines in the Ruy Lopez. The entire strategy here is about the pawn structure - Black would like to clear the way to play …c7-c5, while White hopes to really push forward with their f-pawn. Both sides are fundamentally trying to do the same thing - create a strong central pawn structure. White will try to apply pressure on the d5-pawn from an early stage and can use the d4-square for a knight to create additional pressure.
On the other hand Black will utilize the active knight on e4 and can go for …c5 and …f6 or …f5 pawn breaks for additional play in the center, sometimes using f-file. We are fortunate to have this interesting and under-analyzed opening at our disposal, just waiting to be reinvestigated!