We aim at enhancing the Quality of Service (QoS) management in modern Internet applications that heavily rely on the quality of the underlying network. Our goal is to provide the application developers with mechanisms for specifying and controlling high-level, application-related QoS metrics, rather than the traditional low-level, network-related metrics like latency, throughput, packet loss, etc. We study this problem for the challenging class of Real-Time Online Interactive Applications (ROIA) which include, e.g., multiplayer online games and simulation-based e-learning and training. We leverage the dynamic management features of Software-Defined Networking (SDN) to express, monitor and control applications' QoS demands. Our particular contributions are as follows: 1) we propose a Northbound API for specifying the application-level QoS requirements in ROIA, 2) we demonstrate how the application-level metric "response time" can be automatically translated into network-level metrics understood by the SDN controller, and 3) we report experimental results on managing application-level QoS in an example online game on an OpenFlow-enabled testbed.