Research into defensive functioning in psychotherapy has thus far focused on patients’ defense use. However, also the defensive functioning of therapists might be significant because of its potential in promoting changes in the patient’s overall defensive functioning by sharing their higher-level understanding of a given situation and letting the patient have the opportunity to learn how to cope more successfully. This exploratory case study is the first to examine therapist’s defense mechanisms and their relationship to changes in the patient’s defensive functioning evaluated at different times throughout psychoanalytic treatment. We assessed the use of defense mechanisms with the Defense Mechanisms Rating Scales in 20 sessions collected at three phases (early, middle and late) of the psychoanalytic treatment. For each session, we identified therapist’s and patient’s defenses, defense levels and overall defensive functioning, with particular attention to the sequence of consecutively activated defenses within the therapeutic dyad. Results showed that the patient’s defensive functioning tended to gradually improve over the course of the treatment, with a slight decrease at the end. Therapists’ overall defensive functioning remained stable throughout the treatment with values in the range of high-neurotic and mature defenses. Assessment of the dyadic interaction between therapist and patient’s use of defenses showed that within-session, the patient tended to use the same individual defenses that the therapist used, which was especially pronounced in the initial phases of the treatment. Towards the end of the treatment, once there was a stable shared knowledge, the patient started to explore using new, higher-level defenses on her own, independent from what defenses the therapist used. Our findings emphasized the analyst’s role in encouraging the development of more effective ways of coping in the patient, confirming previous theoretical and empirical research regarding the improvement of patient’s defensive functioning in psychotherapy. The alterations in these coping strategies, also called high-adaptive defenses, as part of the therapist-patient interaction demonstrate the importance of studying defenses as an excellent process-based outcome measure. The measurement of the degree to which the analyst models and illustrates these superior coping methods to the patient is a prime vehicle for supporting internalization of these skills by the patient.