The club-record signing's winner also gives Steve Bruce a first victory as Newcastle head coach as Spurs suffered defeat in 2019/20 for the first time.
The hosts had 80 per cent possession but it was Newcastle who went ahead. Christian Atsu, a substitute for the injured Allan Saint-Maximin, set up Joelinton to strike past Hugo Lloris.
Spurs had Son Heung-min returning from suspension but the South Korean was unable to steer a volley past Newcastle goalkeeper Martin Dubravka.
Lucas Moura and Harry Kane both missed late chances as Newcastle held on for a 22nd Premier League victory over their joint-favourite opponents.
Spurs: 1 Sep v Arsenal (A)
Newcastle: 31 Aug v Watford (H)