[5] He contributed greatly to the refinement of the performances of classical music in Taiwan, leading local musicians to gain recognition overseas.

Four years later, he received a last-minute invitation to stand-in with the Symphony when its conductor, William Steinberg, was taken ill. Held at New York City's Carnegie Hall, the concert brought Mazer to the attention of Sir Georg Solti, who later asked him to be his Associate Conductor of the Chicago Symphony Orchestra, a position he held for the next 15 years.

During that time, he performed with internationally acclaimed musicians such as Arthur Rubinstein, Isaac Stern, Andrés Segovia, Rudolf Serkin, Robert Casadesus, and Marian Anderson.

[14][6] Mazer conducted hundreds of subscription concerts for the Chicago Symphony Orchestra, often substituting for Solti on short notice.

[5] Although initially described alongside Solti as the "new breed of virtuosi,"[15] not every review was positive: following his move to Taiwan, one Chicago critic described his performances as "dull readings.

[6] Mazer was first approached about coming to Taiwan as a guest conductor during his term with the Chicago Symphony and agreed to visit the country for four concerts in the summer of 1985.

[37] In addition to holding "miniconcerts" and lecturing in the Chicago Public Schools,[37] Mazer helped bring "unprepared ghetto children" to concerts.

[2] Mazer makes an extended appearance in Sir Yehudi Menuhin's then-widely read autobiography Unfinished Journey.

[21][39] In Taiwan, through "steely strength"[6] the energetic Mazer insisted on walking despite a serious injury and operation that "would have an ordinary person confined to a wheelchair forever.