In a first-half which Spurs dominated, the visitors took the lead thanks to England striker Defoe, whose scuffed shot from an Aaron Lennon pull back managed to beat Alex McCarthy in the Reading goal on 18 minutes.
The Royals keeper, who was making his Premier League debut, made a couple of strong saves but was guilty of nearly handing Spurs a second, when his poor first touch was latched on to by Defoe, who found Gylfi Sigurdsson but the midfielder's effort was cleared by Alex Pearce off the line.
In the second-half it took a while for Spurs to get going but the game was put to bed on the 71st minute when Defoe capitalised on a Reading error in midfield to drive towards goal before firing the ball past McCarthy.
It was not long before Spurs got their third when Kyle Walker pulled the ball back for Bale who, like Defoe for his first, scuffed his shot into the back of the net on the 74th minute.
Reading pulled a goal back in injury time thanks to substitute Hal Robson-Kanu, who latched on to the end of a cross from Adam Le Fondre, but it was little consolation as Spurs secured their first win of the Premier League season.