its true...sasuke won and left naruto unconcious. i guess he could have killed his most beloved friend, but he wanted to show his brother he was not like him, a murderer. he was going to attain the mangenkyio some other way... atleast those were his toughts then. but it is also true that naruto could have given him a severe punch but all he went for was his forehead protector, because unlike sasuke naruto didnt wanted to kill him. he proved sasuke that he was also strong. 