Who was the first person to call Maharaj by the name 'Sai Baba'?

The person who first greeted Maharaj with the name 'Sai Baba' was a gentleman named Mhalasapati. As detailed in Chapter 0, Mhalasapati was a goldsmith and a devotee of Khandoba living in Shirdi. When Maharaj entered the Khandoba temple wearing a kafni and cap, Mhalasapati spontaneously welcomed him with the words "Aavo Sai Baba," which translates to "Come, Sai Baba." From that moment on, Maharaj held that name, and it is what most of his devotees called him.