"1 e4 e5
2 Nf3 Nc6
3 Bb5 a6
4 Ba4 Nf6
5 O-O Nxe4
6 d4 b5
7 Bb3 d5
8 dxe5 Be6
9 Nbd2 Nc5
10 c3 Be7
11 Bc2 Bg4
...
Then , if it's only to draw , why to choose Open Defence?"

The Bernstein/Karpov 9Nbd2 is black's biggest headache.  GM Victor Mikhalevski has promoted 11...d4!? (instead of 11...Bg4) and it has done pretty well. You might want to take a look at it.

Anand (black) drew Topalov in a critical line after:
1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Ne4 6. d4 b5 7. Bb3 d5 8. de5 Be6 9. Nbd2 Nc5 10. c3 d4 11. Be6 Ne6 12. cd4 Ncd4 13. a4 Bc5!? 14. Ne4 O-O!? 15. Nc5 Nf3 16. Qf3 Nc5 17. ab5 ab5 18. Bg5! Ra1!? 19. Bd8 Rf1 20. Kf1 Rd8 21. g3 Ne6 (drawn on move 30).

I think titled players can study this a little and never lose. At lower levels, either side can slip and fall.

I think black can get good chances in other Open Ruy lines. As a practical matter, you may never face the line given above.

The Open Ruy is not easy to play, but it usually generates sharp and interesting play.