This popular line challenges White's center early.
5. e3.
The line-opening 5. dc is more forthright.
5...Nc6; 6. Nf3 d5; 7. cd N:d5!?
This is playable because White has not yet played a2-a3. Black plays to unbalance the position.
8. Bb5 Qb6; 9. B:c6+ Q:c6; 10. Ne5 Qb5!
This unexpected move holds the a4-e8 diagonal and keeps White from castling.
11. dc B:c3+; 12. bc Q:c5; 13. Bd2.
White tries to hold the pawn, but ...
13...N:e3! 14. B:e3 Q:e5; 15. O-O Bd7; 16. Bd4 Qg5; 17. Rab1? Bc6; 18. f4.
White uses the open lines to mount an attack.
18...Qd5; 19. Rbe1 O-O; 20. f5! ef; 21. R:f5.
Black's kingside has no defenders. Can it be held?
21...Qd7; 22. Re3 Rae8; 23. Rg3 g6; 24. Rh5.
Trying to infiltrate on the h-file. 25. R:h7 is not a threat yet because of 25...K:h7; 26. Rh3+ Q:h3.
24...Re1+; 25. Kf2 Rfe8; 26. R5h3?
This loses at once. But Black threatened 26...Qe6, and 26. Rgh3 would have allowed 26...Qg4.
26...Qf5+! 0:1.
Looks like a blunder, but 27. Q:f5 allows R8e2#. Or 27. Rf3 Q:c2+ and it's over.