A synchronous blend of online learning and "face-to-face" teaching is becoming a feasible instructional approach in higher education with the advent of technology. Although this learning mode is not new in higher education, little research has been done to contextualise social presence experiences in which effects of interactions were explored for enhancing learning. A qualitative approach was adopted using the case study method to examine the instructor and students' pedagogic interactions in the social presence of a blended synchronous learning environment. This paper reports an exploration of the blended learning with an online group of students at a remote site attending a computer-aided engineering drawing course synchronously with a face-to-face group taught by an instructor in a laboratory. The process of interaction was visually and verbally mediated by video-conference as if in an online face-to-face learning community. The findings show that the online and face-to-face groups had different social presence experiences in which interaction emerged. Emotional adaptation and practice is needed for the students and the instructor in such a complex environment. Based on the interaction patterns, a framework of interactions in the blended synchronous learning environment is conceptualised to inform course development and instructional design. Implications for further study are also discussed.