Middle Powers are generally understood to perform diplomatic functions of constructive engagement and consensus-building to facilitate agreement in international negotiations. Middle Powers may, however, adopt more confrontational roles, especially when their accommodative functions become deficient. Whilst theoretical perspectives on Middle Powers account for such roles, limited empirical evidence has been provided to explore the conditions under which they revert to combative diplomacy. This article contributes to this area by examining the role of South Africa in the 2003 Cancun Ministerial Conference of the World Trade Organisation. During this period, South Africa shifted to a more confrontational approach epitomised by the heightening of its public diplomacy against developed countries and its co-leadership of the G-20 coalition of developing countries. The Cancun Ministerial collapse reflected both the possibilities and limitations of combative diplomacy as South Africa enhanced its international prestige but failed to extract any meaningful concessions, whilst triggering the threat of diplomatic retaliation by the major trading powers.