The current zeitgeist in language teacher education dwells on teacher identity regarding it as one of the big buzzwords to explore and critically reflect teacher qualities from a socio-cognitive perspective. Drawing from this current trend, the research intended to disambiguate three English language instructors' sense of self-efficacy, perceptions, professional identity and professional competence in one of the most established and prestigious state universities in the country through the qualitative case study method. After selecting ESP practitioners following convenience sampling, autobiographies, informal dialogues, classroom observations, opening interviews, post-observation interviews, and field notes were utilized to gather data. Having scrutinized the professional identities of instructors through the lens of self-efficacy beliefs, perceptions, and professional competence, the study exposed that professional competence came to the fore being the best mediator to gain awareness of professional teacher identity. However, self-efficacy did not subserve as a predictor in exploring the complexity of teacher identity due to discordance with perceptions and realities of identity issues. Finally, some suggestions for further considerations were stated to be operationalized within the EFL context of in-service language teacher education.