The Premier League outfit were powered to a 2-0 lead at BMO Field by an Erik Lamela brace in the first half.
But second-half strikes to Toronto's Andrew Wiedeman and Jordan Hamilton saw the hosts level in the 73rd minute - only for Andros Townsend to score an 85th-minute winner.
Spurs dominated from the outset, controlling possession and eventually converting their time on the ball to the scoreboard when Lamela first struck.
Right-sided forward Christian Eriksen initiated the foray forward, linking with central striker Roberto Soldado, who laid off to the former Roma man to tuck away a left-footed shot into the right side of the net in the 16th minute.
Defoe was in behind the Spurs' defensive line in the 19th minute, but he was unable to equalise against the side he spent more than nine Premier League seasons with as goalkeeper Brad Friedel came off his line to collect.
Lamela doubled Spurs' lead with a near-identical effort in the 40th minute, having begun the play in central midfield.
The 22-year-old passed a ball through to Aaron Lennon, who found Soldado, and Lamela continued his run and had acres of space to finish the pass from the number nine - and he did so with conviction.
Tottenham manager Mauricio Pochettino changed his entire outfield at half-time including club debutant Ben Davies, who impressed at left-back after only just sealing his move from Swansea.
Toronto coach Ryan Nelsen swung seven changes himself, including Defoe.
Wiedeman pulled a goal back for Toronto, and it was from the same scoring area as where Lamela struck twice in the opening half.
Wiedeman was put through by Daniel Lovitz, who forced a turnover on the halfway line before dancing forward and releasing the goalscorer to put Toronto on the board in the 65th minute.
Hamilton saw the hosts level in the 73rd minute, finishing off a fine move down the middle from the home side.
But Townsend ensured Tottenham would leave victors, with a curling finish into the top-right corner.
Spurs' win saw them successful for the first time on their tour, after a 3-3 draw with Seattle Sounders on Saturday.
