Bale remained at home as speculation about his future mounts but Spurs still named a strong side, with Nacer Chadli handed his first start for Andre Villas-Boas' men.
Monaco, who have invested heavily in their squad as they look to challenge Paris St Germain in the coming season, took the lead after 14 minutes through a well-struck Andrea Raggi volley.
Two goals in quick succession after the interval, courtesy of Lucas Ocampos and Radamel Falcao, put Claudio Ranieri's side well on top.
Spurs struck back just before the hour through young striker Harry Kane but the Premier League side did not have time to get themselves back in to the match.
Falcao added his second with a composed finish, with Mounir Obbadi grabbing the fifth on 70 minutes and Andros Townsend scoring a fine consolation for the visitors late on.