The England man came in to the starting line up in place of Victor Wanyama and did not waste his chance to impress.
He struck in the 9th minute, sweeping into the net after Davinson Sanchez's header from a cross after a short corner.
It was his first goal since he scored in similar fashion away at Burnley at the end of the 2016/17 season.
Tottenham dominated the opening stages of the match and had enjoyed 80% possession in the first 20 minutes.
However Cardiff came back into contention and it took a brilliant intervention from Toby Alderweireld to prevent an equaliser after Jacob Murphy had beaten Hugo Lloris with a dinked effort.