How did the saint who came to Shirdi come to be known as 'Sai Baba'?

The name 'Sai Baba' was bestowed upon him by a man named Mhalasapati. The Introduction in Chapter 0 recounts that when Maharaj, wearing a kafni and cap, first entered the Khandoba temple in Shirdi, Mhalasapati greeted him with the words 'Aavo Sai Baba,' which means 'Come, Sai Baba.' Maharaj adopted this name and it stayed with him for the rest of his life. The text even notes that when his testimony was taken in a commission and he was asked his name, he simply replied, 'They call me Sai Baba.'