e6 or c6 is standard response in this opening or u can play Nf6 which transposes into a grunfield defence.....

 

Well 11. ... Nc6 wouldnt have been better entirely, since you can pin the knight, followed up with the trade, netting a knight extra instead of the pawn.  Moving the pawn to c5 is not always a great move, but in this situation, it worked fine.