Crellin, 55, was in his fifth lap when he crashed at the Mountain Box.
Comments flooded into the Isle of Man Today Web site mourning his loss. (Read his obituary here.)
Crellin was hailed as a modest, decent, gutsy "regular bloke."
"He was the epitome of what the TT was, and still is all about," one friend wrote.
Earlier in the day, Crellin placed third in the first electric motorcycle race around the TT course.
Off the TT course, the transportation engineer was an avid mountaineer. He made three attempts to climb Mount Everest, his last attempt earlier this year.
Between 1998 and 2009, he climbed some of the highest mountains in the world: Elbrus, Kilimanjaro, McKinley, Vinson Massif, Aconcagua, Carstensz Pyramid and Kosciuszko.
Our sympathy and condolences to his family and friends in the Isle of Man and around the globe.