Belgium will play France in the Davis Cup final after coming back from 2-1 down to beat Australia in Brussels.
Nine-time champions France will play 2015 runners-up Belgium on 24-26 November.
Yannick Noah’s side needed only one singles match on Sunday to see off a Serbian side who were without Novak Djokovic.
Underdogs Serbia had picked up an unexpected first point when Lucas Pouille lost to Lajovic in Friday’s singles but Tsonga levelled by beating Davis Cup debutant Laslo Djere.
Pierre-Hugues Herbert and Nicolas Mahut then beat Filip Krajinovic and Nenad Zimonjic in the doubles and Tsonga’s second victory saw them progress.