The clavulanic acid in augmentin works to enhance the action of the amoxicillin by inhibiting the action of bacterial penicillinase.
This rather successful (until antibiotic resistance to it starts getting out of hand) antibiotic thus capitalises on throwing in an agent that inhibits the bacterial adaptation to become resistant to penicillin (of which amoxicillin is a form of), raising the bar for the antibiotic arms war, so as to speak.