Without suspended star Sebastian Giovinco and fellow forward Jozy Altidore, reigning MLS Cup champion Toronto claimed a much-needed win at BMO Field.
Cristian Higuita had canceled out Jay Chapman's second-half opener, but the home side found a winner through Telfer three minutes from time.
After Chapman put away a rebound in the 63rd minute, Orlando equalized through Higuita – who struck from 20 yards.
But Telfer was the hero for Greg Vanney's men.
The 24-year-old's powerful volley from an Auro cross proved to be enough to beat Joe Bendik and land Teller his first MLS goal.
Telfer moved up to Toronto's senior side in 2018 after spending the 2017 season with Toronto FC II.
Toronto has struggled to open the MLS season, with the club having battled its way to the CONCACAF Champions League final.
The win was just TFC's third of the MLS season and lifted the club into ninth in the Eastern Conference, nine points behind fourth-placed Orlando.