Matz Sels was called into action early as he stopped Son Heung-min’s strike from the edge of the box inside just five minutes, before Brennan Johnson fired across goal only to be denied by the goalkeeper again.
Forest were happy playing on the counter, and they took the lead against the run of play just before the half-hour mark.
Anthony Elanga was put through by Morgan Gibbs-White, and he calmly placed his third goal in as many games past Fraser Forster and into the bottom corner.
Spurs pushed for an equaliser before HT, as Johnson forced Sels into another brilliant save before Son struck the side-netting from a free-kick.
Forest were more threatening early in the second half, as Forster came out well to close down Gibbs-White – but Spurs also had further chances to score, as Johnson produced a lovely turn before being denied one-on-one by Sels.
The game was becoming an end-to-end affair, as Nikola Milenković headed over from a corner, before substitute James Maddison struck wide with his weaker left foot.
Forest were resolute defensively though, and they held on for a victory which remarkably lifts them up to third in the table, with Nuno Espirito Santo beating his former employers.
Meanwhile, Spurs’ three-game winning streak against the Tricky Trees came to an end, as Ange Postecoglou’s side disappointingly remain in the bottom half.